[BUG] Modify concatenate_columns ignore_empty output

AUTHORS.md

@@ -112,3 +112,4 @@ Contributors
 - [@asmirnov69](https://github.com/asmirnov69) | [contributions](https://github.com/pyjanitor-devs/pyjanitor/issues?q=is%3Aclosed+mentions%asmirnov69)
 - [@xujiboy](https://github.com/xujiboy) | [contributions](https://github.com/pyjanitor-devs/pyjanitor/issues?q=is%3Aclosed+mentions%xujiboy)
 - [@joranbeasley](https://github.com/joranbeasley) | [contributions](https://github.com/pyjanitor-devs/pyjanitor/issues?q=is%3Aclosed+mentions%joranbeasley)
+- [@Fu-Jie](https://github.com/Fu-Jie) | [contributions](https://github.com/pyjanitor-devs/pyjanitor/pulls?q=is%3Aclosed+mentions%3AFu-Jie)

CHANGELOG.md

@@ -5,6 +5,7 @@
 -   [INF] Replace `pytest.ini` file with `pyproject.toml` file. PR #1204 @Zeroto521
 -   [INF] Extract docstrings tests from all tests. PR #1205 @Zeroto521
 -   [BUG] address the `TypeError` when importing v0.24.0 (issue #1201 @xujiboy and @joranbeasley)
+-   [BUG] Modify ignore_empty output in `concatenate_columns`. Issue #1164 @Fu-Jie
 
 ## [v0.24.0] - 2022-11-12
 

janitor/functions/concatenate_columns.py

@@ -51,8 +51,9 @@ def concatenate_columns(
     if len(column_names) < 2:
         raise JanitorError("At least two columns must be specified")
 
+    df = df.copy()  # avoid mutating original data
     df[new_column_name] = (
-        df[column_names].astype(str).fillna("").agg(sep.join, axis=1)
+        df[column_names].astype("string").fillna("").agg(sep.join, axis=1)
     )
 
     if ignore_empty:

tests/functions/test_concatenate_columns.py

@@ -28,7 +28,7 @@ def test_concatenate_columns_null_values(missingdata_df):
         new_column_name="index",
         ignore_empty=True,
     )
-    expected_values = ["1.0-1", "2.0-2", "nan-3"] * 3
+    expected_values = ["1.0-1", "2.0-2", "3"] * 3
     assert expected_values == df["index"].tolist()