Improve speed of NaturalIdPartitioner (#3276)

Co-authored-by: jafermarq <[email protected]>

datasets/flwr_datasets/partitioner/natural_id_partitioner.py

@@ -17,19 +17,52 @@
 
 from typing import Dict
 
+import numpy as np
+from tqdm import tqdm
+
 import datasets
+from flwr_datasets.common.typing import NDArrayInt
 from flwr_datasets.partitioner.partitioner import Partitioner
 
 
 class NaturalIdPartitioner(Partitioner):
-    """Partitioner for dataset that can be divided by a reference to id in dataset."""
+    """Partitioner for a dataset that can be divided by a column with partition ids.
+
+    Parameters
+    ----------
+    partition_by: str
+        The name of the column that contains the unique values of partitions.
+
+
+    Examples
+    --------
+    "flwrlabs/shakespeare" dataset
+    >>> from flwr_datasets import FederatedDataset
+    >>> from flwr_datasets.partitioner import NaturalIdPartitioner
+    >>>
+    >>> partitioner = NaturalIdPartitioner(partition_by="character_id")
+    >>> fds = FederatedDataset(dataset="flwrlabs/shakespeare",
+    >>>                        partitioners={"train": partitioner})
+    >>> partition = fds.load_partition(0)
+
+    "sentiment140" (aka Twitter) dataset
+    >>> from flwr_datasets import FederatedDataset
+    >>> from flwr_datasets.partitioner import NaturalIdPartitioner
+    >>>
+    >>> partitioner = NaturalIdPartitioner(partition_by="user")
+    >>> fds = FederatedDataset(dataset="sentiment140",
+    >>>                        partitioners={"train": partitioner})
+    >>> partition = fds.load_partition(0)
+    """
 
     def __init__(
         self,
         partition_by: str,
     ):
         super().__init__()
         self._partition_id_to_natural_id: Dict[int, str] = {}
+        self._natural_id_to_partition_id: Dict[str, int] = {}
+        self._partition_id_to_indices: Dict[int, NDArrayInt] = {}
         self._partition_by = partition_by
 
     def _create_int_partition_id_to_natural_id(self) -> None:
@@ -42,6 +75,33 @@ def _create_int_partition_id_to_natural_id(self) -> None:
             zip(range(len(unique_natural_ids)), unique_natural_ids)
         )
 
+    def _create_natural_id_to_int_partition_id(self) -> None:
+        """Create a mapping from unique client ids from dataset to int indices.
+
+        Natural ids come from the column specified in `partition_by`. This object is
+        inverse of the `self._partition_id_to_natural_id`. This method assumes that
+        `self._partition_id_to_natural_id` already exist.
+        """
+        self._natural_id_to_partition_id = {
+            value: key for key, value in self._partition_id_to_natural_id.items()
+        }
+
+    def _create_partition_id_to_indices(self) -> None:
+        natural_id_to_indices = {}  # type: ignore
+        natural_ids = np.array(self.dataset[self._partition_by])
+
+        for index, natural_id in tqdm(
+            enumerate(natural_ids), desc="Generating partition_id_to_indices"
+        ):
+            if natural_id not in natural_id_to_indices:
+                natural_id_to_indices[natural_id] = []
+            natural_id_to_indices[natural_id].append(index)
+
+        self._partition_id_to_indices = {
+            self._natural_id_to_partition_id[natural_id]: indices
+            for natural_id, indices in natural_id_to_indices.items()
+        }
+
     def load_partition(self, partition_id: int) -> datasets.Dataset:
         """Load a single partition corresponding to a single `partition_id`.
 
@@ -60,17 +120,19 @@ def load_partition(self, partition_id: int) -> datasets.Dataset:
         """
         if len(self._partition_id_to_natural_id) == 0:
             self._create_int_partition_id_to_natural_id()
+            self._create_natural_id_to_int_partition_id()
 
-        return self.dataset.filter(
-            lambda row: row[self._partition_by]
-            == self._partition_id_to_natural_id[partition_id]
-        )
+        if len(self._partition_id_to_indices) == 0:
+            self._create_partition_id_to_indices()
+
+        return self.dataset.select(self._partition_id_to_indices[partition_id])
 
     @property
     def num_partitions(self) -> int:
         """Total number of partitions."""
         if len(self._partition_id_to_natural_id) == 0:
             self._create_int_partition_id_to_natural_id()
+            self._create_natural_id_to_int_partition_id()
         return len(self._partition_id_to_natural_id)
 
     @property

datasets/pyproject.toml

@@ -58,6 +58,7 @@ datasets = "^2.14.6"
 pillow = { version = ">=6.2.1", optional = true }
 soundfile = { version = ">=0.12.1", optional = true }
 librosa = { version = ">=0.10.0.post2", optional = true }
+tqdm ="^4.66.1"
 
 [tool.poetry.dev-dependencies]
 isort = "==5.13.2"