FIX-#6752: Preserve dtypes cache on '.insert()'

modin/core/dataframe/pandas/dataframe/dataframe.py

@@ -1327,9 +1327,9 @@
         new_dtypes = self.index.to_frame(name=names).dtypes
         try:
             new_dtypes = ModinDtypes.concat([new_dtypes, self._dtypes])
         except NotImplementedError:
             # can raise on duplicated labels
             new_dtypes = None
 
         # We will also use the `new_column_names` in the calculation of the internal metadata, so this is a
         # lightweight way of ensuring the metadata matches.
@@ -2804,6 +2804,7 @@
         new_index=None,
         new_columns=None,
         keep_remaining=False,
+        new_dtypes=None,
     ):
         """
         Apply a function across an entire axis for a subset of the data.
@@ -2826,6 +2827,10 @@
             advance, and if not provided it must be computed.
         keep_remaining : boolean, default: False
             Whether or not to drop the data that is not computed over.
+        new_dtypes : ModinDtypes or pandas.Series, optional
+            The data types of the result. This is an optimization
+            because there are functions that always result in a particular data
+            type, and allows us to avoid (re)computing it.
 
         Returns
         -------
@@ -2854,7 +2859,9 @@
             new_index = self.index if axis == 1 else None
         if new_columns is None:
             new_columns = self.columns if axis == 0 else None
-        return self.__constructor__(new_partitions, new_index, new_columns, None, None)
+        return self.__constructor__(
+            new_partitions, new_index, new_columns, None, None, dtypes=new_dtypes
+        )
 
     @lazy_metadata_decorator(apply_axis="both")
     def apply_select_indices(

modin/core/storage_formats/pandas/query_compiler.py

@@ -58,7 +58,7 @@
     SeriesGroupByDefault,
 )
 from modin.core.dataframe.base.dataframe.utils import join_columns
-from modin.core.dataframe.pandas.metadata import ModinDtypes
+from modin.core.dataframe.pandas.metadata import DtypesDescriptor, ModinDtypes
 from modin.core.storage_formats.base.query_compiler import BaseQueryCompiler
 from modin.error_message import ErrorMessage
 from modin.utils import (
@@ -731,9 +731,9 @@
                 # concat index dtypes (None, since they're unknown) with column dtypes
                 try:
                     dtypes = ModinDtypes.concat([None, self._modin_frame._dtypes])
                 except NotImplementedError:
                     # may raise on duplicated names in materialized 'self.dtypes'
                     dtypes = None
 
             return self.__constructor__(
                 self._modin_frame.apply_full_axis(
@@ -3112,6 +3112,23 @@
             df.insert(internal_idx, column, value)
             return df
 
+        if hasattr(value, "dtype"):
+            value_dtype = value.dtype
+        elif is_scalar(value):
+            value_dtype = np.dtype(type(value))
+        else:
+            value_dtype = np.array(value).dtype
+
+        new_columns = self.columns.insert(loc, column)
+        new_dtypes = ModinDtypes.concat(
+            [
+                self._modin_frame._dtypes,
+                DtypesDescriptor({column: value_dtype}, cols_with_unknown_dtypes=[]),
+            ]
+        ).lazy_get(
+            new_columns
+        )  # get dtypes in a proper order
+
         # TODO: rework by passing list-like values to `apply_select_indices`
         # as an item to distribute
         new_modin_frame = self._modin_frame.apply_full_axis_select_indices(
@@ -3120,7 +3137,8 @@
             numeric_indices=[loc],
             keep_remaining=True,
             new_index=self.index,
-            new_columns=self.columns.insert(loc, column),
+            new_columns=new_columns,
+            new_dtypes=new_dtypes,
         )
         return self.__constructor__(new_modin_frame)
 

modin/test/storage_formats/pandas/test_internals.py

@@ -1965,6 +1965,61 @@ class TestZeroComputationDtypes:
     Test cases that shouldn't trigger dtypes computation during their execution.
     """
 
+    @pytest.mark.parametrize("self_dtype", ["materialized", "partial", "unknown"])
+    @pytest.mark.parametrize(
+        "value, value_dtype",
+        [
+            [3.5, np.dtype(float)],
+            [[3.5, 2.4], np.dtype(float)],
+            [np.array([3.5, 2.4]), np.dtype(float)],
+            [pd.Series([3.5, 2.4]), np.dtype(float)],
+        ],
+    )
+    def test_preserve_dtypes_insert(self, self_dtype, value, value_dtype):
+        with mock.patch.object(PandasDataframe, "_compute_dtypes") as patch:
+            df = pd.DataFrame({"a": [1, 2], "b": [3, 4]})
+            if self_dtype == "materialized":
+                assert df._query_compiler._modin_frame.has_materialized_dtypes
+            elif self_dtype == "partial":
+                df._query_compiler._modin_frame.set_dtypes_cache(
+                    ModinDtypes(
+                        DtypesDescriptor(
+                            {"a": np.dtype(int)}, cols_with_unknown_dtypes=["b"]
+                        )
+                    )
+                )
+            elif self_dtype == "unknown":
+                df._query_compiler._modin_frame.set_dtypes_cache(None)
+            else:
+                raise NotImplementedError(self_dtype)
+
+            df.insert(loc=0, column="c", value=value)
+
+            if self_dtype == "materialized":
+                result_dtype = pandas.Series(
+                    [value_dtype, np.dtype(int), np.dtype(int)], index=["c", "a", "b"]
+                )
+                assert df._query_compiler._modin_frame.has_materialized_dtypes
+                assert df.dtypes.equals(result_dtype)
+            elif self_dtype == "partial":
+                result_dtype = DtypesDescriptor(
+                    {"a": np.dtype(int), "c": value_dtype},
+                    cols_with_unknown_dtypes=["b"],
+                    columns_order={0: "c", 1: "a", 2: "b"},
+                )
+                df._query_compiler._modin_frame._dtypes._value.equals(result_dtype)
+            elif self_dtype == "unknown":
+                result_dtype = DtypesDescriptor(
+                    {"c": value_dtype},
+                    cols_with_unknown_dtypes=["a", "b"],
+                    columns_order={0: "c", 1: "a", 2: "b"},
+                )
+                df._query_compiler._modin_frame._dtypes._value.equals(result_dtype)
+            else:
+                raise NotImplementedError(self_dtype)
+
+        patch.assert_not_called()
+
     def test_get_dummies_case(self):
         with mock.patch.object(PandasDataframe, "_compute_dtypes") as patch:
             df = pd.DataFrame(