Fix default contiguous value in IidPartitioner (#2406)

---------

Co-authored-by: Taner Topal <[email protected]>

datasets/flwr_datasets/partitioner/iid_partitioner.py

@@ -48,5 +48,5 @@ def load_partition(self, idx: int) -> datasets.Dataset:
  single dataset partition
  """
  return self.dataset.shard(
- num_shards=self._num_partitions, index=idx, contiguous=True
+ num_shards=self._num_partitions, index=idx, contiguous=False
  )

datasets/flwr_datasets/partitioner/iid_partitioner_test.py

@@ -18,6 +18,7 @@
 import unittest
 from typing import Tuple
 
+import numpy as np
 from parameterized import parameterized
 
 from datasets import Dataset
@@ -100,11 +101,16 @@ def test_load_partition_correct_data(
  self, num_partitions: int, num_rows: int
  ) -> None:
  """Test if the data in partition is equal to the expected."""
- _, partitioner = _dummy_setup(num_partitions, num_rows)
- partition_size = num_rows // num_partitions
+ dataset, partitioner = _dummy_setup(num_partitions, num_rows)
  partition_index = 2
  partition = partitioner.load_partition(partition_index)
- self.assertEqual(partition["features"][0], partition_index * partition_size)
+ row_id = 0
+ self.assertEqual(
+ partition["features"][row_id],
+ dataset[np.arange(partition_index, len(dataset), num_partitions)][
+ "features"
+ ][row_id],
+ )
 
  @parameterized.expand( # type: ignore
  [