[EHN] Set expand_column's sep default as "|"

AUTHORS.rst

@@ -101,3 +101,4 @@ Contributors
 - `@MollyCroke <https://github.com/MollyCroke>`_ | `contributions <https://github.com/pyjanitor-devs/pyjanitor/issues?q=is%3Aclosed+mentions%3AMollyCroke>`_
 - `@ericclessantostv <https://github.com/ericlessantostv>`_ | `contributions <https://github.com/pyjanitor-devs/pyjanitor/issues?q=is%3Aclosed+mentions%3Aericclessantostv>`_
 - `@fireddd <https://github.com/fireddd>`_ |  `contributions <https://github.com/pyjanitor-devs/pyjanitor/issues?q=is%3Aclosed+mentions%3Afireddd>`_
+- `@Zeroto521 <https://github.com/Zeroto521>`_ | `contributions <https://github.com/pyjanitor-devs/pyjanitor/pulls?utf8=%E2%9C%93&q=is%3Aclosed+mentions%3Zeroto521>`_

CHANGELOG.md

@@ -1,6 +1,7 @@
 # Changelog
 
 ## [Unreleased]
+
 -   [DOC] Fix references and broken links in AUTHORS.rst. @loganthomas
 -   [DOC] Updated Broken links in the README and contributing docs. @nvamsikrishna05
 -   [INF] Update pre-commit hooks and remove mutable references. Issue #844. @loganthomas
@@ -14,6 +15,7 @@
 -   [DOC] Delete Read the Docs project and remove all readthedocs.io references from the repo. Issue #863. @loganthomas
 -   [DOC] Updated various documentation sources to reflect pyjanitor-dev ownership. @loganthomas
 -   [INF] Fix `isort` automatic checks. Issue #845. @loganthomas
+-   [EHN] Set `expand_column`'s `sep` default is `"|"`, same to `pandas.Series.str.get_dummies`. Issue #876. @Zeroto521
 -   [ENH] Deprecate `limit` from fill_direction. fill_direction now uses kwargs. @samukweku
 
 ## [v0.21.0] - 2021-07-16

janitor/functions.py

@@ -1292,7 +1292,10 @@ def _fill_empty(df, column_names, value=None):  # noqa: F811
 @pf.register_dataframe_method
 @deprecated_alias(column="column_name")
 def expand_column(
-    df: pd.DataFrame, column_name: Hashable, sep: str, concat: bool = True
+    df: pd.DataFrame,
+    column_name: Hashable,
+    sep: str = "|",
+    concat: bool = True,
 ) -> pd.DataFrame:
     """Expand a categorical column with multiple labels into dummy-coded columns.
 
@@ -1319,7 +1322,8 @@ def expand_column(
 
     :param df: A pandas DataFrame.
     :param column_name: Which column to expand.
-    :param sep: The delimiter. Example delimiters include `|`, `, `, `,` etc.
+    :param sep: The delimiter, same to
+        :py:meth:`~pandas.Series.str.get_dummies`'s `sep`, default as `|`.
     :param concat: Whether to return the expanded column concatenated to
         the original dataframe (`concat=True`), or to return it standalone
         (`concat=False`).

tests/functions/test_expand_column.py

@@ -25,3 +25,17 @@ def test_expand_and_concat():
         column_name="col1", sep=", ", concat=True
     )
     assert df.shape[1] == 8
+
+
+@pytest.mark.functions
+def test_sep_default_parameter():
+    """Test that the default parameter is a pipe character `|`."""
+    df = pd.DataFrame(
+        {
+            "col1": ["A|B", "B|C|D", "E|F", "A|E|F"],
+            "col2": [1, 2, 3, 4],
+        }
+    )
+    result = df.expand_column("col1")
+
+    assert result.shape[1] == 8