diff --git a/code/pandas_1_concat-merge-join.ipynb b/code/pandas_1_concat-merge-join.ipynb
index c66e580..117b95c 100644
--- a/code/pandas_1_concat-merge-join.ipynb
+++ b/code/pandas_1_concat-merge-join.ipynb
@@ -2,7 +2,7 @@
  "cells": [
   {
    "cell_type": "code",
-   "execution_count": null,
+   "execution_count": 1,
    "metadata": {},
    "outputs": [],
    "source": [
@@ -114,7 +114,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 5,
+   "execution_count": 4,
    "metadata": {},
    "outputs": [
     {
@@ -194,7 +194,7 @@
        "5  a5  b5  c5"
       ]
      },
-     "execution_count": 5,
+     "execution_count": 4,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -205,10 +205,94 @@
   },
   {
    "cell_type": "code",
-   "execution_count": null,
+   "execution_count": 6,
    "metadata": {},
-   "outputs": [],
-   "source": []
+   "outputs": [
+    {
+     "data": {
+      "text/html": [
+       "<div>\n",
+       "<style scoped>\n",
+       "    .dataframe tbody tr th:only-of-type {\n",
+       "        vertical-align: middle;\n",
+       "    }\n",
+       "\n",
+       "    .dataframe tbody tr th {\n",
+       "        vertical-align: top;\n",
+       "    }\n",
+       "\n",
+       "    .dataframe thead th {\n",
+       "        text-align: right;\n",
+       "    }\n",
+       "</style>\n",
+       "<table border=\"1\" class=\"dataframe\">\n",
+       "  <thead>\n",
+       "    <tr style=\"text-align: right;\">\n",
+       "      <th></th>\n",
+       "      <th>D</th>\n",
+       "      <th>E</th>\n",
+       "      <th>F</th>\n",
+       "    </tr>\n",
+       "  </thead>\n",
+       "  <tbody>\n",
+       "    <tr>\n",
+       "      <th>0</th>\n",
+       "      <td>d0</td>\n",
+       "      <td>e0</td>\n",
+       "      <td>f0</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>1</th>\n",
+       "      <td>d1</td>\n",
+       "      <td>e1</td>\n",
+       "      <td>f1</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>2</th>\n",
+       "      <td>d2</td>\n",
+       "      <td>e2</td>\n",
+       "      <td>f2</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>3</th>\n",
+       "      <td>d3</td>\n",
+       "      <td>e3</td>\n",
+       "      <td>f3</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>4</th>\n",
+       "      <td>d4</td>\n",
+       "      <td>e4</td>\n",
+       "      <td>f4</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>5</th>\n",
+       "      <td>d5</td>\n",
+       "      <td>e5</td>\n",
+       "      <td>f5</td>\n",
+       "    </tr>\n",
+       "  </tbody>\n",
+       "</table>\n",
+       "</div>"
+      ],
+      "text/plain": [
+       "    D   E   F\n",
+       "0  d0  e0  f0\n",
+       "1  d1  e1  f1\n",
+       "2  d2  e2  f2\n",
+       "3  d3  e3  f3\n",
+       "4  d4  e4  f4\n",
+       "5  d5  e5  f5"
+      ]
+     },
+     "execution_count": 6,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "pd.concat([df3,df4])"
+   ]
   },
   {
    "cell_type": "markdown",
@@ -223,10 +307,175 @@
   },
   {
    "cell_type": "code",
-   "execution_count": null,
+   "execution_count": 48,
    "metadata": {},
-   "outputs": [],
-   "source": []
+   "outputs": [
+    {
+     "data": {
+      "text/html": [
+       "<div>\n",
+       "<style scoped>\n",
+       "    .dataframe tbody tr th:only-of-type {\n",
+       "        vertical-align: middle;\n",
+       "    }\n",
+       "\n",
+       "    .dataframe tbody tr th {\n",
+       "        vertical-align: top;\n",
+       "    }\n",
+       "\n",
+       "    .dataframe thead th {\n",
+       "        text-align: right;\n",
+       "    }\n",
+       "</style>\n",
+       "<table border=\"1\" class=\"dataframe\">\n",
+       "  <thead>\n",
+       "    <tr style=\"text-align: right;\">\n",
+       "      <th></th>\n",
+       "      <th>A</th>\n",
+       "      <th>B</th>\n",
+       "      <th>C</th>\n",
+       "      <th>D</th>\n",
+       "      <th>E</th>\n",
+       "      <th>F</th>\n",
+       "    </tr>\n",
+       "  </thead>\n",
+       "  <tbody>\n",
+       "    <tr>\n",
+       "      <th>0</th>\n",
+       "      <td>a0</td>\n",
+       "      <td>b0</td>\n",
+       "      <td>c0</td>\n",
+       "      <td>NaN</td>\n",
+       "      <td>NaN</td>\n",
+       "      <td>NaN</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>1</th>\n",
+       "      <td>a1</td>\n",
+       "      <td>b1</td>\n",
+       "      <td>c1</td>\n",
+       "      <td>NaN</td>\n",
+       "      <td>NaN</td>\n",
+       "      <td>NaN</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>2</th>\n",
+       "      <td>a2</td>\n",
+       "      <td>b2</td>\n",
+       "      <td>c2</td>\n",
+       "      <td>NaN</td>\n",
+       "      <td>NaN</td>\n",
+       "      <td>NaN</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>3</th>\n",
+       "      <td>a3</td>\n",
+       "      <td>b3</td>\n",
+       "      <td>c3</td>\n",
+       "      <td>NaN</td>\n",
+       "      <td>NaN</td>\n",
+       "      <td>NaN</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>4</th>\n",
+       "      <td>a4</td>\n",
+       "      <td>b4</td>\n",
+       "      <td>c4</td>\n",
+       "      <td>NaN</td>\n",
+       "      <td>NaN</td>\n",
+       "      <td>NaN</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>5</th>\n",
+       "      <td>a5</td>\n",
+       "      <td>b5</td>\n",
+       "      <td>c5</td>\n",
+       "      <td>NaN</td>\n",
+       "      <td>NaN</td>\n",
+       "      <td>NaN</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>0</th>\n",
+       "      <td>NaN</td>\n",
+       "      <td>NaN</td>\n",
+       "      <td>NaN</td>\n",
+       "      <td>d0</td>\n",
+       "      <td>e0</td>\n",
+       "      <td>f0</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>1</th>\n",
+       "      <td>NaN</td>\n",
+       "      <td>NaN</td>\n",
+       "      <td>NaN</td>\n",
+       "      <td>d1</td>\n",
+       "      <td>e1</td>\n",
+       "      <td>f1</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>2</th>\n",
+       "      <td>NaN</td>\n",
+       "      <td>NaN</td>\n",
+       "      <td>NaN</td>\n",
+       "      <td>d2</td>\n",
+       "      <td>e2</td>\n",
+       "      <td>f2</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>3</th>\n",
+       "      <td>NaN</td>\n",
+       "      <td>NaN</td>\n",
+       "      <td>NaN</td>\n",
+       "      <td>d3</td>\n",
+       "      <td>e3</td>\n",
+       "      <td>f3</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>4</th>\n",
+       "      <td>NaN</td>\n",
+       "      <td>NaN</td>\n",
+       "      <td>NaN</td>\n",
+       "      <td>d4</td>\n",
+       "      <td>e4</td>\n",
+       "      <td>f4</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>5</th>\n",
+       "      <td>NaN</td>\n",
+       "      <td>NaN</td>\n",
+       "      <td>NaN</td>\n",
+       "      <td>d5</td>\n",
+       "      <td>e5</td>\n",
+       "      <td>f5</td>\n",
+       "    </tr>\n",
+       "  </tbody>\n",
+       "</table>\n",
+       "</div>"
+      ],
+      "text/plain": [
+       "     A    B    C    D    E    F\n",
+       "0   a0   b0   c0  NaN  NaN  NaN\n",
+       "1   a1   b1   c1  NaN  NaN  NaN\n",
+       "2   a2   b2   c2  NaN  NaN  NaN\n",
+       "3   a3   b3   c3  NaN  NaN  NaN\n",
+       "4   a4   b4   c4  NaN  NaN  NaN\n",
+       "5   a5   b5   c5  NaN  NaN  NaN\n",
+       "0  NaN  NaN  NaN   d0   e0   f0\n",
+       "1  NaN  NaN  NaN   d1   e1   f1\n",
+       "2  NaN  NaN  NaN   d2   e2   f2\n",
+       "3  NaN  NaN  NaN   d3   e3   f3\n",
+       "4  NaN  NaN  NaN   d4   e4   f4\n",
+       "5  NaN  NaN  NaN   d5   e5   f5"
+      ]
+     },
+     "execution_count": 48,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "pd.concat([df1, df2, df3, df4])"
+   ]
   },
   {
    "cell_type": "markdown",
@@ -244,56 +493,858 @@
   },
   {
    "cell_type": "code",
-   "execution_count": null,
-   "metadata": {},
-   "outputs": [],
-   "source": []
-  },
-  {
-   "cell_type": "code",
-   "execution_count": null,
-   "metadata": {},
-   "outputs": [],
-   "source": []
-  },
-  {
-   "cell_type": "markdown",
-   "metadata": {},
-   "source": [
-    "## Merging and Joining\n",
-    "\n",
-    "Pandas has two functions for joining datasets: `merge()` and `join()`. They perform the same task but have different options and syntax. \n",
-    "\n",
-    "Below is an example of `merge` and `join`.     \n",
-    "HINT (uses the column that repeats in both dataframes )"
-   ]
-  },
-  {
-   "cell_type": "markdown",
-   "metadata": {},
-   "source": [
-    "https://pandas.pydata.org/docs/reference/api/pandas.DataFrame.merge.html"
-   ]
-  },
-  {
-   "cell_type": "code",
-   "execution_count": 7,
+   "execution_count": 9,
    "metadata": {},
-   "outputs": [],
+   "outputs": [
+    {
+     "data": {
+      "text/html": [
+       "<div>\n",
+       "<style scoped>\n",
+       "    .dataframe tbody tr th:only-of-type {\n",
+       "        vertical-align: middle;\n",
+       "    }\n",
+       "\n",
+       "    .dataframe tbody tr th {\n",
+       "        vertical-align: top;\n",
+       "    }\n",
+       "\n",
+       "    .dataframe thead th {\n",
+       "        text-align: right;\n",
+       "    }\n",
+       "</style>\n",
+       "<table border=\"1\" class=\"dataframe\">\n",
+       "  <thead>\n",
+       "    <tr style=\"text-align: right;\">\n",
+       "      <th></th>\n",
+       "      <th>A</th>\n",
+       "      <th>B</th>\n",
+       "      <th>C</th>\n",
+       "      <th>D</th>\n",
+       "      <th>E</th>\n",
+       "      <th>F</th>\n",
+       "    </tr>\n",
+       "  </thead>\n",
+       "  <tbody>\n",
+       "    <tr>\n",
+       "      <th>0</th>\n",
+       "      <td>a0</td>\n",
+       "      <td>b0</td>\n",
+       "      <td>c0</td>\n",
+       "      <td>NaN</td>\n",
+       "      <td>NaN</td>\n",
+       "      <td>NaN</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>1</th>\n",
+       "      <td>a1</td>\n",
+       "      <td>b1</td>\n",
+       "      <td>c1</td>\n",
+       "      <td>NaN</td>\n",
+       "      <td>NaN</td>\n",
+       "      <td>NaN</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>2</th>\n",
+       "      <td>a2</td>\n",
+       "      <td>b2</td>\n",
+       "      <td>c2</td>\n",
+       "      <td>NaN</td>\n",
+       "      <td>NaN</td>\n",
+       "      <td>NaN</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>3</th>\n",
+       "      <td>a3</td>\n",
+       "      <td>b3</td>\n",
+       "      <td>c3</td>\n",
+       "      <td>NaN</td>\n",
+       "      <td>NaN</td>\n",
+       "      <td>NaN</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>4</th>\n",
+       "      <td>a4</td>\n",
+       "      <td>b4</td>\n",
+       "      <td>c4</td>\n",
+       "      <td>NaN</td>\n",
+       "      <td>NaN</td>\n",
+       "      <td>NaN</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>5</th>\n",
+       "      <td>a5</td>\n",
+       "      <td>b5</td>\n",
+       "      <td>c5</td>\n",
+       "      <td>NaN</td>\n",
+       "      <td>NaN</td>\n",
+       "      <td>NaN</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>6</th>\n",
+       "      <td>NaN</td>\n",
+       "      <td>NaN</td>\n",
+       "      <td>NaN</td>\n",
+       "      <td>d0</td>\n",
+       "      <td>e0</td>\n",
+       "      <td>f0</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>7</th>\n",
+       "      <td>NaN</td>\n",
+       "      <td>NaN</td>\n",
+       "      <td>NaN</td>\n",
+       "      <td>d1</td>\n",
+       "      <td>e1</td>\n",
+       "      <td>f1</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>8</th>\n",
+       "      <td>NaN</td>\n",
+       "      <td>NaN</td>\n",
+       "      <td>NaN</td>\n",
+       "      <td>d2</td>\n",
+       "      <td>e2</td>\n",
+       "      <td>f2</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>9</th>\n",
+       "      <td>NaN</td>\n",
+       "      <td>NaN</td>\n",
+       "      <td>NaN</td>\n",
+       "      <td>d3</td>\n",
+       "      <td>e3</td>\n",
+       "      <td>f3</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>10</th>\n",
+       "      <td>NaN</td>\n",
+       "      <td>NaN</td>\n",
+       "      <td>NaN</td>\n",
+       "      <td>d4</td>\n",
+       "      <td>e4</td>\n",
+       "      <td>f4</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>11</th>\n",
+       "      <td>NaN</td>\n",
+       "      <td>NaN</td>\n",
+       "      <td>NaN</td>\n",
+       "      <td>d5</td>\n",
+       "      <td>e5</td>\n",
+       "      <td>f5</td>\n",
+       "    </tr>\n",
+       "  </tbody>\n",
+       "</table>\n",
+       "</div>"
+      ],
+      "text/plain": [
+       "      A    B    C    D    E    F\n",
+       "0    a0   b0   c0  NaN  NaN  NaN\n",
+       "1    a1   b1   c1  NaN  NaN  NaN\n",
+       "2    a2   b2   c2  NaN  NaN  NaN\n",
+       "3    a3   b3   c3  NaN  NaN  NaN\n",
+       "4    a4   b4   c4  NaN  NaN  NaN\n",
+       "5    a5   b5   c5  NaN  NaN  NaN\n",
+       "6   NaN  NaN  NaN   d0   e0   f0\n",
+       "7   NaN  NaN  NaN   d1   e1   f1\n",
+       "8   NaN  NaN  NaN   d2   e2   f2\n",
+       "9   NaN  NaN  NaN   d3   e3   f3\n",
+       "10  NaN  NaN  NaN   d4   e4   f4\n",
+       "11  NaN  NaN  NaN   d5   e5   f5"
+      ]
+     },
+     "execution_count": 9,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "pd.concat([df1, df2, df3, df4], ignore_index=True)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Merging and Joining\n",
+    "\n",
+    "Pandas has two functions for joining datasets: `merge()` and `join()`. They perform the same task but have different options and syntax. \n",
+    "\n",
+    "Below is an example of `merge` and `join`.     \n",
+    "HINT (uses the column that repeats in both dataframes )"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "https://pandas.pydata.org/docs/reference/api/pandas.DataFrame.merge.html"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 11,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "left = pd.DataFrame({'idx': ['i'+str(x) for x in range(3)],\n",
+    "                     'A': ['a'+str(x) for x in range(3)],\n",
+    "                     'B': ['b'+str(x) for x in range(3)]})\n",
+    "\n",
+    "\n",
+    "right = pd.DataFrame({'idx': ['i'+str(x) for x in range(1,4)],\n",
+    "                     'C': ['c'+str(x) for x in range(1,4)],\n",
+    "                     'D': ['d'+str(x) for x in range(1,4)]})"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 22,
+   "metadata": {},
+   "outputs": [
+    {
+     "data": {
+      "text/html": [
+       "<div>\n",
+       "<style scoped>\n",
+       "    .dataframe tbody tr th:only-of-type {\n",
+       "        vertical-align: middle;\n",
+       "    }\n",
+       "\n",
+       "    .dataframe tbody tr th {\n",
+       "        vertical-align: top;\n",
+       "    }\n",
+       "\n",
+       "    .dataframe thead th {\n",
+       "        text-align: right;\n",
+       "    }\n",
+       "</style>\n",
+       "<table border=\"1\" class=\"dataframe\">\n",
+       "  <thead>\n",
+       "    <tr style=\"text-align: right;\">\n",
+       "      <th></th>\n",
+       "      <th>idx</th>\n",
+       "      <th>A</th>\n",
+       "      <th>B</th>\n",
+       "    </tr>\n",
+       "  </thead>\n",
+       "  <tbody>\n",
+       "    <tr>\n",
+       "      <th>0</th>\n",
+       "      <td>i0</td>\n",
+       "      <td>a0</td>\n",
+       "      <td>b0</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>1</th>\n",
+       "      <td>i1</td>\n",
+       "      <td>a1</td>\n",
+       "      <td>b1</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>2</th>\n",
+       "      <td>i2</td>\n",
+       "      <td>a2</td>\n",
+       "      <td>b2</td>\n",
+       "    </tr>\n",
+       "  </tbody>\n",
+       "</table>\n",
+       "</div>"
+      ],
+      "text/plain": [
+       "  idx   A   B\n",
+       "0  i0  a0  b0\n",
+       "1  i1  a1  b1\n",
+       "2  i2  a2  b2"
+      ]
+     },
+     "execution_count": 22,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "left"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 23,
+   "metadata": {},
+   "outputs": [
+    {
+     "data": {
+      "text/html": [
+       "<div>\n",
+       "<style scoped>\n",
+       "    .dataframe tbody tr th:only-of-type {\n",
+       "        vertical-align: middle;\n",
+       "    }\n",
+       "\n",
+       "    .dataframe tbody tr th {\n",
+       "        vertical-align: top;\n",
+       "    }\n",
+       "\n",
+       "    .dataframe thead th {\n",
+       "        text-align: right;\n",
+       "    }\n",
+       "</style>\n",
+       "<table border=\"1\" class=\"dataframe\">\n",
+       "  <thead>\n",
+       "    <tr style=\"text-align: right;\">\n",
+       "      <th></th>\n",
+       "      <th>idx</th>\n",
+       "      <th>C</th>\n",
+       "      <th>D</th>\n",
+       "    </tr>\n",
+       "  </thead>\n",
+       "  <tbody>\n",
+       "    <tr>\n",
+       "      <th>0</th>\n",
+       "      <td>i1</td>\n",
+       "      <td>c1</td>\n",
+       "      <td>d1</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>1</th>\n",
+       "      <td>i2</td>\n",
+       "      <td>c2</td>\n",
+       "      <td>d2</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>2</th>\n",
+       "      <td>i3</td>\n",
+       "      <td>c3</td>\n",
+       "      <td>d3</td>\n",
+       "    </tr>\n",
+       "  </tbody>\n",
+       "</table>\n",
+       "</div>"
+      ],
+      "text/plain": [
+       "  idx   C   D\n",
+       "0  i1  c1  d1\n",
+       "1  i2  c2  d2\n",
+       "2  i3  c3  d3"
+      ]
+     },
+     "execution_count": 23,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "right"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "`join` is identical to `merge`. But when using join, we need to explicitly set the index column of the dataframes to join using `set_index`:"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "https://pandas.pydata.org/docs/reference/api/pandas.DataFrame.join.html"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 31,
+   "metadata": {},
+   "outputs": [
+    {
+     "data": {
+      "text/html": [
+       "<div>\n",
+       "<style scoped>\n",
+       "    .dataframe tbody tr th:only-of-type {\n",
+       "        vertical-align: middle;\n",
+       "    }\n",
+       "\n",
+       "    .dataframe tbody tr th {\n",
+       "        vertical-align: top;\n",
+       "    }\n",
+       "\n",
+       "    .dataframe thead th {\n",
+       "        text-align: right;\n",
+       "    }\n",
+       "</style>\n",
+       "<table border=\"1\" class=\"dataframe\">\n",
+       "  <thead>\n",
+       "    <tr style=\"text-align: right;\">\n",
+       "      <th></th>\n",
+       "      <th>A</th>\n",
+       "      <th>B</th>\n",
+       "      <th>C</th>\n",
+       "      <th>D</th>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>idx</th>\n",
+       "      <th></th>\n",
+       "      <th></th>\n",
+       "      <th></th>\n",
+       "      <th></th>\n",
+       "    </tr>\n",
+       "  </thead>\n",
+       "  <tbody>\n",
+       "    <tr>\n",
+       "      <th>i0</th>\n",
+       "      <td>a0</td>\n",
+       "      <td>b0</td>\n",
+       "      <td>NaN</td>\n",
+       "      <td>NaN</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>i1</th>\n",
+       "      <td>a1</td>\n",
+       "      <td>b1</td>\n",
+       "      <td>c1</td>\n",
+       "      <td>d1</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>i2</th>\n",
+       "      <td>a2</td>\n",
+       "      <td>b2</td>\n",
+       "      <td>c2</td>\n",
+       "      <td>d2</td>\n",
+       "    </tr>\n",
+       "  </tbody>\n",
+       "</table>\n",
+       "</div>"
+      ],
+      "text/plain": [
+       "      A   B    C    D\n",
+       "idx                  \n",
+       "i0   a0  b0  NaN  NaN\n",
+       "i1   a1  b1   c1   d1\n",
+       "i2   a2  b2   c2   d2"
+      ]
+     },
+     "execution_count": 31,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "left_join = left.set_index('idx').join(right.set_index('idx'))\n",
+    "left_join"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "And you see, `join` disregards the row of `right` with the unmatching index `i3`. It retains the row of `left` with the unmatching index `i0` but uses `NaN` for the missing data after joining."
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "#### There are other options we can explore with the `merge()` and `join()` functions. \n",
+    "\n",
+    "Specifically, we can specify `how`. This argument in the function tells us whether we are performing an inner, left, right, or outer join.\n",
+    "\n",
+    "We can also specify a different column for joining in the `merge()` function using the `left_on` and `right_on` arguments. Check out the following documentations if you want to explore more:\n",
+    "\n",
+    "[pandas.DataFrame.merge](https://pandas.pydata.org/pandas-docs/stable/generated/pandas.DataFrame.merge.html)\n",
+    "\n",
+    "[pandas.DataFrame.join](https://pandas.pydata.org/pandas-docs/stable/generated/pandas.DataFrame.join.html)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Bonus Question\n",
+    "\n",
+    "Now if you look back on `merge` and `join`, you realize that in order to perform these functions on a set of dataframes, these dataframes must share a common column as the index. Only rows that have the same index values will be joined. This is similar to the [`join` function in MySQL](https://www.w3schools.com/sql/sql_join.asp), isn't it?\n",
+    "\n",
+    "The bonus question for you is to figure out how to join and concatenate `df1`, `df2`, `df3`, and `df4` we created at the beginning of this challenge. Your end product should look like this:\n",
+    "\n",
+    "![df1-2-3-4.png](../images/df1-2-3-4.png)"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 11,
+   "metadata": {},
+   "outputs": [
+    {
+     "data": {
+      "text/html": [
+       "<div>\n",
+       "<style scoped>\n",
+       "    .dataframe tbody tr th:only-of-type {\n",
+       "        vertical-align: middle;\n",
+       "    }\n",
+       "\n",
+       "    .dataframe tbody tr th {\n",
+       "        vertical-align: top;\n",
+       "    }\n",
+       "\n",
+       "    .dataframe thead th {\n",
+       "        text-align: right;\n",
+       "    }\n",
+       "</style>\n",
+       "<table border=\"1\" class=\"dataframe\">\n",
+       "  <thead>\n",
+       "    <tr style=\"text-align: right;\">\n",
+       "      <th></th>\n",
+       "      <th>A</th>\n",
+       "      <th>B</th>\n",
+       "      <th>C</th>\n",
+       "    </tr>\n",
+       "  </thead>\n",
+       "  <tbody>\n",
+       "    <tr>\n",
+       "      <th>0</th>\n",
+       "      <td>a0</td>\n",
+       "      <td>b0</td>\n",
+       "      <td>c0</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>1</th>\n",
+       "      <td>a1</td>\n",
+       "      <td>b1</td>\n",
+       "      <td>c1</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>2</th>\n",
+       "      <td>a2</td>\n",
+       "      <td>b2</td>\n",
+       "      <td>c2</td>\n",
+       "    </tr>\n",
+       "  </tbody>\n",
+       "</table>\n",
+       "</div>"
+      ],
+      "text/plain": [
+       "    A   B   C\n",
+       "0  a0  b0  c0\n",
+       "1  a1  b1  c1\n",
+       "2  a2  b2  c2"
+      ]
+     },
+     "execution_count": 11,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "df1"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 12,
+   "metadata": {},
+   "outputs": [
+    {
+     "data": {
+      "text/html": [
+       "<div>\n",
+       "<style scoped>\n",
+       "    .dataframe tbody tr th:only-of-type {\n",
+       "        vertical-align: middle;\n",
+       "    }\n",
+       "\n",
+       "    .dataframe tbody tr th {\n",
+       "        vertical-align: top;\n",
+       "    }\n",
+       "\n",
+       "    .dataframe thead th {\n",
+       "        text-align: right;\n",
+       "    }\n",
+       "</style>\n",
+       "<table border=\"1\" class=\"dataframe\">\n",
+       "  <thead>\n",
+       "    <tr style=\"text-align: right;\">\n",
+       "      <th></th>\n",
+       "      <th>A</th>\n",
+       "      <th>B</th>\n",
+       "      <th>C</th>\n",
+       "    </tr>\n",
+       "  </thead>\n",
+       "  <tbody>\n",
+       "    <tr>\n",
+       "      <th>3</th>\n",
+       "      <td>a3</td>\n",
+       "      <td>b3</td>\n",
+       "      <td>c3</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>4</th>\n",
+       "      <td>a4</td>\n",
+       "      <td>b4</td>\n",
+       "      <td>c4</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>5</th>\n",
+       "      <td>a5</td>\n",
+       "      <td>b5</td>\n",
+       "      <td>c5</td>\n",
+       "    </tr>\n",
+       "  </tbody>\n",
+       "</table>\n",
+       "</div>"
+      ],
+      "text/plain": [
+       "    A   B   C\n",
+       "3  a3  b3  c3\n",
+       "4  a4  b4  c4\n",
+       "5  a5  b5  c5"
+      ]
+     },
+     "execution_count": 12,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "df2"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 32,
+   "metadata": {},
+   "outputs": [
+    {
+     "data": {
+      "text/html": [
+       "<div>\n",
+       "<style scoped>\n",
+       "    .dataframe tbody tr th:only-of-type {\n",
+       "        vertical-align: middle;\n",
+       "    }\n",
+       "\n",
+       "    .dataframe tbody tr th {\n",
+       "        vertical-align: top;\n",
+       "    }\n",
+       "\n",
+       "    .dataframe thead th {\n",
+       "        text-align: right;\n",
+       "    }\n",
+       "</style>\n",
+       "<table border=\"1\" class=\"dataframe\">\n",
+       "  <thead>\n",
+       "    <tr style=\"text-align: right;\">\n",
+       "      <th></th>\n",
+       "      <th>D</th>\n",
+       "      <th>E</th>\n",
+       "      <th>F</th>\n",
+       "    </tr>\n",
+       "  </thead>\n",
+       "  <tbody>\n",
+       "    <tr>\n",
+       "      <th>0</th>\n",
+       "      <td>d0</td>\n",
+       "      <td>e0</td>\n",
+       "      <td>f0</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>1</th>\n",
+       "      <td>d1</td>\n",
+       "      <td>e1</td>\n",
+       "      <td>f1</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>2</th>\n",
+       "      <td>d2</td>\n",
+       "      <td>e2</td>\n",
+       "      <td>f2</td>\n",
+       "    </tr>\n",
+       "  </tbody>\n",
+       "</table>\n",
+       "</div>"
+      ],
+      "text/plain": [
+       "    D   E   F\n",
+       "0  d0  e0  f0\n",
+       "1  d1  e1  f1\n",
+       "2  d2  e2  f2"
+      ]
+     },
+     "execution_count": 32,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "df3"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 33,
+   "metadata": {},
+   "outputs": [
+    {
+     "data": {
+      "text/html": [
+       "<div>\n",
+       "<style scoped>\n",
+       "    .dataframe tbody tr th:only-of-type {\n",
+       "        vertical-align: middle;\n",
+       "    }\n",
+       "\n",
+       "    .dataframe tbody tr th {\n",
+       "        vertical-align: top;\n",
+       "    }\n",
+       "\n",
+       "    .dataframe thead th {\n",
+       "        text-align: right;\n",
+       "    }\n",
+       "</style>\n",
+       "<table border=\"1\" class=\"dataframe\">\n",
+       "  <thead>\n",
+       "    <tr style=\"text-align: right;\">\n",
+       "      <th></th>\n",
+       "      <th>D</th>\n",
+       "      <th>E</th>\n",
+       "      <th>F</th>\n",
+       "    </tr>\n",
+       "  </thead>\n",
+       "  <tbody>\n",
+       "    <tr>\n",
+       "      <th>3</th>\n",
+       "      <td>d3</td>\n",
+       "      <td>e3</td>\n",
+       "      <td>f3</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>4</th>\n",
+       "      <td>d4</td>\n",
+       "      <td>e4</td>\n",
+       "      <td>f4</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>5</th>\n",
+       "      <td>d5</td>\n",
+       "      <td>e5</td>\n",
+       "      <td>f5</td>\n",
+       "    </tr>\n",
+       "  </tbody>\n",
+       "</table>\n",
+       "</div>"
+      ],
+      "text/plain": [
+       "    D   E   F\n",
+       "3  d3  e3  f3\n",
+       "4  d4  e4  f4\n",
+       "5  d5  e5  f5"
+      ]
+     },
+     "execution_count": 33,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "df4"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 36,
+   "metadata": {},
+   "outputs": [
+    {
+     "data": {
+      "text/html": [
+       "<div>\n",
+       "<style scoped>\n",
+       "    .dataframe tbody tr th:only-of-type {\n",
+       "        vertical-align: middle;\n",
+       "    }\n",
+       "\n",
+       "    .dataframe tbody tr th {\n",
+       "        vertical-align: top;\n",
+       "    }\n",
+       "\n",
+       "    .dataframe thead th {\n",
+       "        text-align: right;\n",
+       "    }\n",
+       "</style>\n",
+       "<table border=\"1\" class=\"dataframe\">\n",
+       "  <thead>\n",
+       "    <tr style=\"text-align: right;\">\n",
+       "      <th></th>\n",
+       "      <th>A</th>\n",
+       "      <th>B</th>\n",
+       "      <th>C</th>\n",
+       "    </tr>\n",
+       "  </thead>\n",
+       "  <tbody>\n",
+       "    <tr>\n",
+       "      <th>0</th>\n",
+       "      <td>a0</td>\n",
+       "      <td>b0</td>\n",
+       "      <td>c0</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>1</th>\n",
+       "      <td>a1</td>\n",
+       "      <td>b1</td>\n",
+       "      <td>c1</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>2</th>\n",
+       "      <td>a2</td>\n",
+       "      <td>b2</td>\n",
+       "      <td>c2</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>3</th>\n",
+       "      <td>a3</td>\n",
+       "      <td>b3</td>\n",
+       "      <td>c3</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>4</th>\n",
+       "      <td>a4</td>\n",
+       "      <td>b4</td>\n",
+       "      <td>c4</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>5</th>\n",
+       "      <td>a5</td>\n",
+       "      <td>b5</td>\n",
+       "      <td>c5</td>\n",
+       "    </tr>\n",
+       "  </tbody>\n",
+       "</table>\n",
+       "</div>"
+      ],
+      "text/plain": [
+       "    A   B   C\n",
+       "0  a0  b0  c0\n",
+       "1  a1  b1  c1\n",
+       "2  a2  b2  c2\n",
+       "3  a3  b3  c3\n",
+       "4  a4  b4  c4\n",
+       "5  a5  b5  c5"
+      ]
+     },
+     "execution_count": 36,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
    "source": [
-    "left = pd.DataFrame({'idx': ['i'+str(x) for x in range(3)],\n",
-    "                     'A': ['a'+str(x) for x in range(3)],\n",
-    "                     'B': ['b'+str(x) for x in range(3)]})\n",
-    "\n",
-    "\n",
-    "right = pd.DataFrame({'idx': ['i'+str(x) for x in range(1,4)],\n",
-    "                     'C': ['c'+str(x) for x in range(1,4)],\n",
-    "                     'D': ['d'+str(x) for x in range(1,4)]})"
+    "concat12 = pd.concat([df1,df2])\n",
+    "concat12"
    ]
   },
   {
    "cell_type": "code",
-   "execution_count": 8,
+   "execution_count": 37,
    "metadata": {},
    "outputs": [
     {
@@ -317,54 +1368,78 @@
        "  <thead>\n",
        "    <tr style=\"text-align: right;\">\n",
        "      <th></th>\n",
-       "      <th>idx</th>\n",
-       "      <th>A</th>\n",
-       "      <th>B</th>\n",
+       "      <th>D</th>\n",
+       "      <th>E</th>\n",
+       "      <th>F</th>\n",
        "    </tr>\n",
        "  </thead>\n",
        "  <tbody>\n",
        "    <tr>\n",
        "      <th>0</th>\n",
-       "      <td>i0</td>\n",
-       "      <td>a0</td>\n",
-       "      <td>b0</td>\n",
+       "      <td>d0</td>\n",
+       "      <td>e0</td>\n",
+       "      <td>f0</td>\n",
        "    </tr>\n",
        "    <tr>\n",
        "      <th>1</th>\n",
-       "      <td>i1</td>\n",
-       "      <td>a1</td>\n",
-       "      <td>b1</td>\n",
+       "      <td>d1</td>\n",
+       "      <td>e1</td>\n",
+       "      <td>f1</td>\n",
        "    </tr>\n",
        "    <tr>\n",
        "      <th>2</th>\n",
-       "      <td>i2</td>\n",
-       "      <td>a2</td>\n",
-       "      <td>b2</td>\n",
+       "      <td>d2</td>\n",
+       "      <td>e2</td>\n",
+       "      <td>f2</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>3</th>\n",
+       "      <td>d3</td>\n",
+       "      <td>e3</td>\n",
+       "      <td>f3</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>4</th>\n",
+       "      <td>d4</td>\n",
+       "      <td>e4</td>\n",
+       "      <td>f4</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>5</th>\n",
+       "      <td>d5</td>\n",
+       "      <td>e5</td>\n",
+       "      <td>f5</td>\n",
        "    </tr>\n",
        "  </tbody>\n",
        "</table>\n",
        "</div>"
       ],
       "text/plain": [
-       "  idx   A   B\n",
-       "0  i0  a0  b0\n",
-       "1  i1  a1  b1\n",
-       "2  i2  a2  b2"
+       "    D   E   F\n",
+       "0  d0  e0  f0\n",
+       "1  d1  e1  f1\n",
+       "2  d2  e2  f2\n",
+       "3  d3  e3  f3\n",
+       "4  d4  e4  f4\n",
+       "5  d5  e5  f5"
       ]
      },
-     "execution_count": 8,
+     "execution_count": 37,
      "metadata": {},
      "output_type": "execute_result"
     }
    ],
    "source": [
-    "left"
+    "concat34 = pd.concat([df3,df4])\n",
+    "concat34"
    ]
   },
   {
    "cell_type": "code",
-   "execution_count": 9,
-   "metadata": {},
+   "execution_count": 40,
+   "metadata": {
+    "scrolled": true
+   },
    "outputs": [
     {
      "data": {
@@ -387,116 +1462,82 @@
        "  <thead>\n",
        "    <tr style=\"text-align: right;\">\n",
        "      <th></th>\n",
-       "      <th>idx</th>\n",
+       "      <th>A</th>\n",
+       "      <th>B</th>\n",
        "      <th>C</th>\n",
-       "      <th>D</th>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>Index</th>\n",
+       "      <th></th>\n",
+       "      <th></th>\n",
+       "      <th></th>\n",
        "    </tr>\n",
        "  </thead>\n",
        "  <tbody>\n",
        "    <tr>\n",
        "      <th>0</th>\n",
-       "      <td>i1</td>\n",
-       "      <td>c1</td>\n",
-       "      <td>d1</td>\n",
+       "      <td>a0</td>\n",
+       "      <td>b0</td>\n",
+       "      <td>c0</td>\n",
        "    </tr>\n",
        "    <tr>\n",
        "      <th>1</th>\n",
-       "      <td>i2</td>\n",
-       "      <td>c2</td>\n",
-       "      <td>d2</td>\n",
+       "      <td>a1</td>\n",
+       "      <td>b1</td>\n",
+       "      <td>c1</td>\n",
        "    </tr>\n",
        "    <tr>\n",
        "      <th>2</th>\n",
-       "      <td>i3</td>\n",
+       "      <td>a2</td>\n",
+       "      <td>b2</td>\n",
+       "      <td>c2</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>3</th>\n",
+       "      <td>a3</td>\n",
+       "      <td>b3</td>\n",
        "      <td>c3</td>\n",
-       "      <td>d3</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>4</th>\n",
+       "      <td>a4</td>\n",
+       "      <td>b4</td>\n",
+       "      <td>c4</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>5</th>\n",
+       "      <td>a5</td>\n",
+       "      <td>b5</td>\n",
+       "      <td>c5</td>\n",
        "    </tr>\n",
        "  </tbody>\n",
        "</table>\n",
        "</div>"
       ],
       "text/plain": [
-       "  idx   C   D\n",
-       "0  i1  c1  d1\n",
-       "1  i2  c2  d2\n",
-       "2  i3  c3  d3"
+       "        A   B   C\n",
+       "Index            \n",
+       "0      a0  b0  c0\n",
+       "1      a1  b1  c1\n",
+       "2      a2  b2  c2\n",
+       "3      a3  b3  c3\n",
+       "4      a4  b4  c4\n",
+       "5      a5  b5  c5"
       ]
      },
-     "execution_count": 9,
+     "execution_count": 40,
      "metadata": {},
      "output_type": "execute_result"
     }
    ],
    "source": [
-    "right"
-   ]
-  },
-  {
-   "cell_type": "markdown",
-   "metadata": {},
-   "source": [
-    "`join` is identical to `merge`. But when using join, we need to explicitly set the index column of the dataframes to join using `set_index`:"
-   ]
-  },
-  {
-   "cell_type": "markdown",
-   "metadata": {},
-   "source": [
-    "https://pandas.pydata.org/docs/reference/api/pandas.DataFrame.join.html"
-   ]
-  },
-  {
-   "cell_type": "code",
-   "execution_count": null,
-   "metadata": {},
-   "outputs": [],
-   "source": []
-  },
-  {
-   "cell_type": "markdown",
-   "metadata": {},
-   "source": [
-    "And you see, `join` disregards the row of `right` with the unmatching index `i3`. It retains the row of `left` with the unmatching index `i0` but uses `NaN` for the missing data after joining."
-   ]
-  },
-  {
-   "cell_type": "markdown",
-   "metadata": {},
-   "source": [
-    "#### There are other options we can explore with the `merge()` and `join()` functions. \n",
-    "\n",
-    "Specifically, we can specify `how`. This argument in the function tells us whether we are performing an inner, left, right, or outer join.\n",
-    "\n",
-    "We can also specify a different column for joining in the `merge()` function using the `left_on` and `right_on` arguments. Check out the following documentations if you want to explore more:\n",
-    "\n",
-    "[pandas.DataFrame.merge](https://pandas.pydata.org/pandas-docs/stable/generated/pandas.DataFrame.merge.html)\n",
-    "\n",
-    "[pandas.DataFrame.join](https://pandas.pydata.org/pandas-docs/stable/generated/pandas.DataFrame.join.html)"
-   ]
-  },
-  {
-   "cell_type": "markdown",
-   "metadata": {},
-   "source": [
-    "## Bonus Question\n",
-    "\n",
-    "Now if you look back on `merge` and `join`, you realize that in order to perform these functions on a set of dataframes, these dataframes must share a common column as the index. Only rows that have the same index values will be joined. This is similar to the [`join` function in MySQL](https://www.w3schools.com/sql/sql_join.asp), isn't it?\n",
-    "\n",
-    "The bonus question for you is to figure out how to join and concatenate `df1`, `df2`, `df3`, and `df4` we created at the beginning of this challenge. Your end product should look like this:\n",
-    "\n",
-    "![df1-2-3-4.png](../images/df1-2-3-4.png)"
+    "concat12_a = concat12.rename_axis(\"Index\")\n",
+    "concat12_a"
    ]
   },
   {
    "cell_type": "code",
-   "execution_count": null,
-   "metadata": {},
-   "outputs": [],
-   "source": []
-  },
-  {
-   "cell_type": "code",
-   "execution_count": 11,
+   "execution_count": 41,
    "metadata": {},
    "outputs": [
     {
@@ -520,53 +1561,82 @@
        "  <thead>\n",
        "    <tr style=\"text-align: right;\">\n",
        "      <th></th>\n",
-       "      <th>A</th>\n",
-       "      <th>B</th>\n",
-       "      <th>C</th>\n",
+       "      <th>D</th>\n",
+       "      <th>E</th>\n",
+       "      <th>F</th>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>Index</th>\n",
+       "      <th></th>\n",
+       "      <th></th>\n",
+       "      <th></th>\n",
        "    </tr>\n",
        "  </thead>\n",
        "  <tbody>\n",
        "    <tr>\n",
        "      <th>0</th>\n",
-       "      <td>a0</td>\n",
-       "      <td>b0</td>\n",
-       "      <td>c0</td>\n",
+       "      <td>d0</td>\n",
+       "      <td>e0</td>\n",
+       "      <td>f0</td>\n",
        "    </tr>\n",
        "    <tr>\n",
        "      <th>1</th>\n",
-       "      <td>a1</td>\n",
-       "      <td>b1</td>\n",
-       "      <td>c1</td>\n",
+       "      <td>d1</td>\n",
+       "      <td>e1</td>\n",
+       "      <td>f1</td>\n",
        "    </tr>\n",
        "    <tr>\n",
        "      <th>2</th>\n",
-       "      <td>a2</td>\n",
-       "      <td>b2</td>\n",
-       "      <td>c2</td>\n",
+       "      <td>d2</td>\n",
+       "      <td>e2</td>\n",
+       "      <td>f2</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>3</th>\n",
+       "      <td>d3</td>\n",
+       "      <td>e3</td>\n",
+       "      <td>f3</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>4</th>\n",
+       "      <td>d4</td>\n",
+       "      <td>e4</td>\n",
+       "      <td>f4</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>5</th>\n",
+       "      <td>d5</td>\n",
+       "      <td>e5</td>\n",
+       "      <td>f5</td>\n",
        "    </tr>\n",
        "  </tbody>\n",
        "</table>\n",
        "</div>"
       ],
       "text/plain": [
-       "    A   B   C\n",
-       "0  a0  b0  c0\n",
-       "1  a1  b1  c1\n",
-       "2  a2  b2  c2"
+       "        D   E   F\n",
+       "Index            \n",
+       "0      d0  e0  f0\n",
+       "1      d1  e1  f1\n",
+       "2      d2  e2  f2\n",
+       "3      d3  e3  f3\n",
+       "4      d4  e4  f4\n",
+       "5      d5  e5  f5"
       ]
      },
-     "execution_count": 11,
+     "execution_count": 41,
      "metadata": {},
      "output_type": "execute_result"
     }
    ],
    "source": [
-    "df1"
+    "concat34_a = concat34.rename_axis(\"Index\")\n",
+    "concat34_a"
    ]
   },
   {
    "cell_type": "code",
-   "execution_count": 12,
+   "execution_count": 53,
    "metadata": {},
    "outputs": [
     {
@@ -593,53 +1663,99 @@
        "      <th>A</th>\n",
        "      <th>B</th>\n",
        "      <th>C</th>\n",
+       "      <th>D</th>\n",
+       "      <th>E</th>\n",
+       "      <th>F</th>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>Index</th>\n",
+       "      <th></th>\n",
+       "      <th></th>\n",
+       "      <th></th>\n",
+       "      <th></th>\n",
+       "      <th></th>\n",
+       "      <th></th>\n",
        "    </tr>\n",
        "  </thead>\n",
        "  <tbody>\n",
        "    <tr>\n",
+       "      <th>0</th>\n",
+       "      <td>a0</td>\n",
+       "      <td>b0</td>\n",
+       "      <td>c0</td>\n",
+       "      <td>d0</td>\n",
+       "      <td>e0</td>\n",
+       "      <td>f0</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>1</th>\n",
+       "      <td>a1</td>\n",
+       "      <td>b1</td>\n",
+       "      <td>c1</td>\n",
+       "      <td>d1</td>\n",
+       "      <td>e1</td>\n",
+       "      <td>f1</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>2</th>\n",
+       "      <td>a2</td>\n",
+       "      <td>b2</td>\n",
+       "      <td>c2</td>\n",
+       "      <td>d2</td>\n",
+       "      <td>e2</td>\n",
+       "      <td>f2</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
        "      <th>3</th>\n",
        "      <td>a3</td>\n",
        "      <td>b3</td>\n",
        "      <td>c3</td>\n",
+       "      <td>d3</td>\n",
+       "      <td>e3</td>\n",
+       "      <td>f3</td>\n",
        "    </tr>\n",
        "    <tr>\n",
        "      <th>4</th>\n",
        "      <td>a4</td>\n",
        "      <td>b4</td>\n",
        "      <td>c4</td>\n",
+       "      <td>d4</td>\n",
+       "      <td>e4</td>\n",
+       "      <td>f4</td>\n",
        "    </tr>\n",
        "    <tr>\n",
        "      <th>5</th>\n",
        "      <td>a5</td>\n",
        "      <td>b5</td>\n",
        "      <td>c5</td>\n",
+       "      <td>d5</td>\n",
+       "      <td>e5</td>\n",
+       "      <td>f5</td>\n",
        "    </tr>\n",
        "  </tbody>\n",
        "</table>\n",
        "</div>"
       ],
       "text/plain": [
-       "    A   B   C\n",
-       "3  a3  b3  c3\n",
-       "4  a4  b4  c4\n",
-       "5  a5  b5  c5"
+       "        A   B   C   D   E   F\n",
+       "Index                        \n",
+       "0      a0  b0  c0  d0  e0  f0\n",
+       "1      a1  b1  c1  d1  e1  f1\n",
+       "2      a2  b2  c2  d2  e2  f2\n",
+       "3      a3  b3  c3  d3  e3  f3\n",
+       "4      a4  b4  c4  d4  e4  f4\n",
+       "5      a5  b5  c5  d5  e5  f5"
       ]
      },
-     "execution_count": 12,
+     "execution_count": 53,
      "metadata": {},
      "output_type": "execute_result"
     }
    ],
    "source": [
-    "df2"
+    "final_concat = pd.concat([concat12_a, concat34_a], axis = 1)\n",
+    "final_concat"
    ]
-  },
-  {
-   "cell_type": "code",
-   "execution_count": null,
-   "metadata": {},
-   "outputs": [],
-   "source": []
   }
  ],
  "metadata": {
@@ -658,7 +1774,7 @@
    "name": "python",
    "nbconvert_exporter": "python",
    "pygments_lexer": "ipython3",
-   "version": "3.9.12"
+   "version": "3.11.4"
   },
   "toc": {
    "base_numbering": 1,