Add test case for applying a function to a groupby object that append… (pandas-dev#53138)

* Add test case for applying a function to a groupby object that appends each group to a list without using copy() function. The test checks if the groups are correctly appended to the list. This resolves GH issue 17718.

* installed pre-commit

* update expected_value

* update expected and installed pre-commit

* test commit

* committing update for expected value from my last verified commit

* update expected_value to  pd.DataFrame({index: [0] * 10, 0: [1] * 10}, index=pd.RangeIndex(0, 100, step=10))

---------

Co-authored-by: Ido Ronen <[email protected]>

Author: 2 people

pandas/tests/groupby/test_apply.py

@@ -19,6 +19,23 @@
 from pandas.tests.groupby import get_groupby_method_args
 
 
+def test_apply_func_that_appends_group_to_list_without_copy():
+    # GH: 17718
+
+    df = DataFrame(1, index=list(range(10)) * 10, columns=[0]).reset_index()
+    groups = []
+
+    def store(group):
+        groups.append(group)
+
+    df.groupby("index").apply(store)
+    expected_value = DataFrame(
+        {"index": [0] * 10, 0: [1] * 10}, index=pd.RangeIndex(0, 100, 10)
+    )
+
+    tm.assert_frame_equal(groups[0], expected_value)
+
+
 def test_apply_issues():
     # GH 5788