Fix issue of 24.12 RC [skip ci] (#826)

Additional changes to fix issue of 24.12 RC based on
#822

NOTE: this PR must be merged as `create a merge commit`

python/src/spark_rapids_ml/umap.py

@@ -790,8 +790,9 @@ class UMAP(UMAPClass, _CumlEstimatorSupervised, _UMAPCumlParams):
 
     sample_fraction : float (optional, default=1.0)
         The fraction of the dataset to be used for fitting the model. Since fitting is done on a single node, very large
-        datasets must be subsampled to fit within the node's memory and execute in a reasonable time. Smaller fractions
-        will result in faster training, but may result in sub-optimal embeddings.
+        datasets must be subsampled to fit within the node's memory. Smaller fractions will result in faster training, but
+        may decrease embedding quality. Note: this is not guaranteed to provide exactly the fraction specified of the total
+        count of the given DataFrame.
 
     featuresCol: str or List[str]
         The feature column names, spark-rapids-ml supports vector, array and columnar as the input.\n
@@ -1463,22 +1464,30 @@ def write_sparse_array(array: scipy.sparse.spmatrix, df_dir: str) -> None:
                 schema=indices_data_schema,
             )
 
-            indptr_df.write.parquet(
-                os.path.join(df_dir, "indptr.parquet"), mode="overwrite"
-            )
-            indices_data_df.write.parquet(
-                os.path.join(df_dir, "indices_data.parquet"), mode="overwrite"
-            )
+            indptr_df.write.parquet(os.path.join(df_dir, "indptr.parquet"))
+            indices_data_df.write.parquet(os.path.join(df_dir, "indices_data.parquet"))
 
         def write_dense_array(array: np.ndarray, df_path: str) -> None:
+            assert (
+                spark.conf.get("spark.sql.execution.arrow.pyspark.enabled") == "true"
+            ), "spark.sql.execution.arrow.pyspark.enabled must be set to true to persist array attributes"
+
             schema = StructType(
                 [
-                    StructField(f"_{i}", FloatType(), False)
-                    for i in range(1, array.shape[1] + 1)
+                    StructField("row_id", LongType(), False),
+                    StructField("data", ArrayType(FloatType(), False), False),
                 ]
             )
-            data_df = spark.createDataFrame(pd.DataFrame(array), schema=schema)
-            data_df.write.parquet(df_path, mode="overwrite")
+            data_df = spark.createDataFrame(
+                pd.DataFrame(
+                    {
+                        "row_id": range(array.shape[0]),
+                        "data": list(array),
+                    }
+                ),
+                schema=schema,
+            )
+            data_df.write.parquet(df_path)
 
         DefaultParamsWriter.saveMetadata(
             self.instance,
@@ -1491,12 +1500,12 @@ def write_dense_array(array: np.ndarray, df_path: str) -> None:
             },
         )
 
+        # get a copy, since we're going to modify the array attributes
         model_attributes = self.instance._get_model_attributes()
         assert model_attributes is not None
+        model_attributes = model_attributes.copy()
 
         data_path = os.path.join(path, "data")
-        if not os.path.exists(data_path):
-            os.makedirs(data_path)
 
         for key in ["embedding_", "raw_data_"]:
             array = model_attributes[key]
@@ -1547,8 +1556,10 @@ def read_sparse_array(
             return scipy.sparse.csr_matrix((data, indices, indptr), shape=csr_shape)
 
         def read_dense_array(df_path: str) -> np.ndarray:
-            data_df = spark.read.parquet(df_path)
-            return np.array(data_df.collect(), dtype=np.float32)
+            data_df = spark.read.parquet(df_path).orderBy("row_id")
+            pdf = data_df.toPandas()
+            assert type(pdf) == pd.DataFrame
+            return np.array(list(pdf.data), dtype=np.float32)
 
         metadata = DefaultParamsReader.loadMetadata(path, self.sc)
         data_path = os.path.join(path, "data")

python/tests/test_umap.py

@@ -1,5 +1,5 @@
 #
-# Copyright (c) 2024, NVIDIA CORPORATION.
+# Copyright (c) 2025, NVIDIA CORPORATION.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -18,7 +18,6 @@
 from typing import Any, Dict, List, Optional, Tuple, Union
 
 import cupy as cp
-import cupyx
 import numpy as np
 import pytest
 import scipy
@@ -415,6 +414,9 @@ def test_umap_copy() -> None:
 def test_umap_model_persistence(
     sparse_fit: bool, gpu_number: int, tmp_path: str
 ) -> None:
+    import os
+    import re
+
     import pyspark
     from packaging import version
 
@@ -459,7 +461,42 @@ def test_umap_model_persistence(
         path = tmp_path + "/umap_tests"
         model_path = f"{path}/umap_model"
         umap_model.write().overwrite().save(model_path)
+
+        try:
+            umap_model.write().save(model_path)
+            assert False, "Overwriting should not be permitted"
+        except Exception as e:
+            assert re.search(r"Output directory .* already exists", str(e))
+
+        # double check expected files/directories
+        model_dir_contents = os.listdir(model_path)
+        data_dir_contents = os.listdir(f"{model_path}/data")
+        assert set(model_dir_contents) == {"data", "metadata"}
+        if sparse_fit:
+            assert set(data_dir_contents) == {
+                "metadata.json",
+                "embedding_.parquet",
+                "raw_data_csr",
+            }
+            assert set(os.listdir(f"{model_path}/data/raw_data_csr")) == {
+                "indptr.parquet",
+                "indices_data.parquet",
+            }
+        else:
+            assert set(data_dir_contents) == {
+                "metadata.json",
+                "embedding_.parquet",
+                "raw_data_.parquet",
+            }
+
+        # make sure we can overwrite
+        umap_model._cuml_params["n_neighbors"] = 10
+        umap_model._cuml_params["set_op_mix_ratio"] = 0.4
+        umap_model.write().overwrite().save(model_path)
+
         umap_model_loaded = UMAPModel.load(model_path)
+        assert umap_model_loaded._cuml_params["n_neighbors"] == 10
+        assert umap_model_loaded._cuml_params["set_op_mix_ratio"] == 0.4
         _assert_umap_model(umap_model_loaded, input_raw_data)