updated readme.md with kurtosis example

README.md

@@ -77,10 +77,20 @@ SELECT min_by(x, y) FROM VALUES (1, 10), (2, 5), (3, 15), (4, 8) as tab(x, y);
 -- | 2                   |
 -- +---------------------+
 
+-- Get the kurtosis value of a column of numeric data.
+SELECT kurtosis(col) FROM VALUES (1.0), (10.0), (100.0), (10.0), (1.0) as tab(col);
+-- Results in
+- +-------------------+
+- "| kurtosis(tab.col) |"
+- +-------------------+
+- "| 4.777292927667962 |"
+- +-------------------+
+
 ```
 
 ## Done
 
 - [x] `mode(expression) -> scalar` - Returns the most frequent (mode) value from a column of data.
 - [x] `max_by(expression1, expression2) -> scalar` - Returns the value of `expression1` associated with the maximum value of `expression2`.
 - [x] `min_by(expression1, expression2) -> scalar` - Returns the value of `expression1` associated with the minimum value of `expression2`.
+- [x] `kurtosis(expression) -> scalar` - Returns the kurtosis, a measure of the `tailedness` of the distribution, for the given numeric values in `expression`.

src/lib.rs

@@ -26,17 +26,24 @@ use datafusion::logical_expr::AggregateUDF;
 #[macro_use]
 pub mod macros;
 pub mod common;
+pub mod kurtosis;
 pub mod max_min_by;
 pub mod mode;
 
 pub mod expr_extra_fn {
+    pub use super::kurtosis::kurtosis;
     pub use super::max_min_by::max_by;
     pub use super::max_min_by::min_by;
     pub use super::mode::mode;
 }
 
 pub fn all_extra_aggregate_functions() -> Vec<Arc<AggregateUDF>> {
-    vec![mode_udaf(), max_min_by::max_by_udaf(), max_min_by::min_by_udaf(), kurtosis::kurtosis_udaf()]
+    vec![
+        mode_udaf(),
+        max_min_by::max_by_udaf(),
+        max_min_by::min_by_udaf(),
+        kurtosis::kurtosis_udaf(),
+    ]
 }
 
 /// Registers all enabled packages with a [`FunctionRegistry`]