change cached collect to cached repr

daft/dataframe/dataframe.py

@@ -1145,7 +1145,6 @@ def collect(self, num_preview_rows: Optional[int] = 8) -> "DataFrame":
 
     def _construct_show_display(self, n: int) -> "DataFrameDisplay":
         """Helper for .show() which will construct the underlying DataFrameDisplay object"""
-        self._populate_preview()
         preview_partition = self._preview.preview_partition
         total_rows = self._preview.dataframe_num_rows
 

tests/dataframe/test_show.py

@@ -24,3 +24,51 @@ def test_show_some(make_df, valid_data, data_source):
     elif variant == "arrow":
         assert df_display.preview.dataframe_num_rows == len(valid_data)
     assert df_display.num_rows == 1
+
+
+def test_show_from_cached_repr(make_df, valid_data):
+    df = make_df(valid_data)
+    df = df.collect()
+    df.__repr__()
+    collected_preview = df._preview
+    df_display = df._construct_show_display(8)
+
+    # Check that cached preview from df.__repr__() was used.
+    assert df_display.preview is collected_preview
+    assert df_display.schema == df.schema()
+    assert len(df_display.preview.preview_partition) == len(valid_data)
+    assert df_display.preview.dataframe_num_rows == 3
+    assert df_display.num_rows == 3
+
+
+def test_show_from_cached_repr_prefix(make_df, valid_data):
+    df = make_df(valid_data)
+    df = df.collect(3)
+    df.__repr__()
+    df_display = df._construct_show_display(2)
+
+    assert df_display.schema == df.schema()
+    assert len(df_display.preview.preview_partition) == 2
+    # Check that a prefix of the cached preview from df.__repr__() was used, so dataframe_num_rows should be set.
+    assert df_display.preview.dataframe_num_rows == 3
+    assert df_display.num_rows == 2
+
+
+def test_show_not_from_cached_repr(make_df, valid_data, data_source):
+    df = make_df(valid_data)
+    df = df.collect(2)
+    df.__repr__()
+    collected_preview = df._preview
+    df_display = df._construct_show_display(8)
+
+    variant = data_source
+    if variant == "parquet":
+        # Cached preview from df.__repr__() is NOT USED because data was not materialized from parquet.
+        assert df_display.preview != collected_preview
+    elif variant == "arrow":
+        # Cached preview from df.__repr__() is USED because data was materialized from arrow.
+        assert df_display.preview == collected_preview
+    assert df_display.schema == df.schema()
+    assert len(df_display.preview.preview_partition) == len(valid_data)
+    assert df_display.preview.dataframe_num_rows == 3
+    assert df_display.num_rows == 3