Fixes #3762: Fix dataframe groupby aggregations when keys contain NaNs

This PR (fixes #3762) using dataframe groupby with keys that contain `NaN`s would cause the aggregations to fail. To resolve this, we mask out the values that belong to the `NaN` segment

arkouda/dataframe.py

@@ -4,6 +4,7 @@
 import os
 import random
 from collections import UserDict
+from functools import reduce
 from typing import Callable, Dict, List, Optional, Tuple, Union, cast
 from warnings import warn
 
@@ -24,10 +25,11 @@
 from arkouda.join import inner_join
 from arkouda.numpy import cast as akcast
 from arkouda.numpy import cumsum, where
-from arkouda.numpy.dtypes import bigint
+from arkouda.numpy.dtypes import _is_dtype_in_union, bigint
 from arkouda.numpy.dtypes import bool_ as akbool
 from arkouda.numpy.dtypes import float64 as akfloat64
 from arkouda.numpy.dtypes import int64 as akint64
+from arkouda.numpy.dtypes import numeric_scalars
 from arkouda.numpy.dtypes import uint64 as akuint64
 from arkouda.pdarrayclass import RegistrationError, pdarray
 from arkouda.pdarraycreation import arange, array, create_pdarray, full, zeros
@@ -104,14 +106,48 @@ class DataFrameGroupBy:
         If True the grouped values of the aggregation keys will be treated as an index.
     """
 
-    def __init__(self, gb, df, gb_key_names=None, as_index=True):
+    def __init__(self, gb, df, gb_key_names=None, as_index=True, dropna=True):
+
         self.gb = gb
         self.df = df
         self.gb_key_names = gb_key_names
         self.as_index = as_index
         for attr in ["nkeys", "permutation", "unique_keys", "segments"]:
             setattr(self, attr, getattr(gb, attr))
 
+        self.dropna = dropna
+        self.where_not_nan = None
+        self.all_non_nan = False
+
+        if dropna:
+            from arkouda import all as ak_all
+            from arkouda import isnan
+
+            # calculate ~isnan on each key then & them all together
+            # keep up with if they're all_non_nan, so we can skip indexing later
+            key_cols = (
+                [df[k] for k in gb_key_names] if isinstance(gb_key_names, List) else [df[gb_key_names]]
+            )
+            where_key_not_nan = [
+                ~isnan(col)
+                for col in key_cols
+                if isinstance(col, pdarray) and _is_dtype_in_union(col.dtype, numeric_scalars)
+            ]
+
+            if len(where_key_not_nan) == 0:
+                # if empty then none of the keys are pdarray, so non are nan
+                self.all_non_nan = True
+            else:
+                self.where_not_nan = reduce(lambda x, y: x & y, where_key_not_nan)
+                self.all_non_nan = ak_all(self.where_not_nan)
+
+    def _get_df_col(self, c):
+        # helper function to mask out the values where the keys are nan when dropna is True
+        if not self.dropna or self.all_non_nan:
+            return self.df.data[c]
+        else:
+            return self.df.data[c][self.where_not_nan]
+
     @classmethod
     def _make_aggop(cls, opname):
         numerical_dtypes = [akfloat64, akint64, akuint64]
@@ -148,18 +184,18 @@ def aggop(self, colnames=None):
             if isinstance(colnames, List):
                 if isinstance(self.gb_key_names, str):
                     return DataFrame(
-                        {c: self.gb.aggregate(self.df.data[c], opname)[1] for c in colnames},
+                        {c: self.gb.aggregate(self._get_df_col(c), opname)[1] for c in colnames},
                         index=Index(self.gb.unique_keys, name=self.gb_key_names),
                     )
                 elif isinstance(self.gb_key_names, list) and len(self.gb_key_names) == 1:
                     return DataFrame(
-                        {c: self.gb.aggregate(self.df.data[c], opname)[1] for c in colnames},
+                        {c: self.gb.aggregate(self._get_df_col(c), opname)[1] for c in colnames},
                         index=Index(self.gb.unique_keys, name=self.gb_key_names[0]),
                     )
                 elif isinstance(self.gb_key_names, list):
                     column_dict = dict(zip(self.gb_key_names, self.unique_keys))
                     for c in colnames:
-                        column_dict[c] = self.gb.aggregate(self.df.data[c], opname)[1]
+                        column_dict[c] = self.gb.aggregate(self._get_df_col(c), opname)[1]
                     return DataFrame(column_dict)
                 else:
                     return None
@@ -2678,7 +2714,7 @@ def GroupBy(self, keys, use_series=False, as_index=True, dropna=True):
 
         gb = akGroupBy(cols, dropna=dropna)
         if use_series:
-            gb = DataFrameGroupBy(gb, self, gb_key_names=keys, as_index=as_index)
+            gb = DataFrameGroupBy(gb, self, gb_key_names=keys, as_index=as_index, dropna=dropna)
         return gb
 
     def memory_usage(self, index=True, unit="B") -> Series:

tests/dataframe_test.py

@@ -1,7 +1,5 @@
-import glob
 import itertools
 import os
-import tempfile
 
 import numpy as np
 import pandas as pd
@@ -664,6 +662,35 @@ def test_gb_aggregations_with_nans(self, agg):
         pd_result = getattr(pd_df.groupby(group_on, as_index=False), agg)()
         assert_frame_equal(ak_result.to_pandas(retain_index=True), pd_result)
 
+        # TODO aggregations of string columns not currently supported (even for count)
+        df.drop("key1", axis=1, inplace=True)
+        df.drop("key2", axis=1, inplace=True)
+        pd_df = df.to_pandas()
+
+        group_on = ["nums1", "nums2"]
+        ak_result = getattr(df.groupby(group_on), agg)()
+        pd_result = getattr(pd_df.groupby(group_on, as_index=False), agg)()
+        assert_frame_equal(ak_result.to_pandas(retain_index=True), pd_result)
+
+        # TODO aggregation mishandling NaN see issue #3765
+        df.drop("nums2", axis=1, inplace=True)
+        pd_df = df.to_pandas()
+        group_on = "nums1"
+        ak_result = getattr(df.groupby(group_on), agg)()
+        pd_result = getattr(pd_df.groupby(group_on), agg)()
+        assert_frame_equal(ak_result.to_pandas(retain_index=True), pd_result)
+
+    def test_count_nan_bug(self):
+        # verify reproducer for #3762 is fixed
+        df = ak.DataFrame({"A": [1, 2, 2, np.nan], "B": [3, 4, 5, 6], "C": [1, np.nan, 2, 3]})
+        ak_result = df.groupby("A").count()
+        pd_result = df.to_pandas().groupby("A").count()
+        assert_frame_equal(ak_result.to_pandas(retain_index=True), pd_result)
+
+        ak_result = df.groupby(["A", "C"], as_index=False).count()
+        pd_result = df.to_pandas().groupby(["A", "C"], as_index=False).count()
+        assert_frame_equal(ak_result.to_pandas(retain_index=True), pd_result)
+
     def test_gb_aggregations_return_dataframe(self):
         ak_df = self.build_ak_df_example2()
         pd_df = ak_df.to_pandas(retain_index=True)