[BUG] Modify concatenate_columns ignore_empty output

AUTHORS.md

@@ -109,3 +109,4 @@ Contributors
 - [@ethompsy](https://github.com/ethompsy) | [contributions](https://github.com/pyjanitor-devs/pyjanitor/issues?q=is%3Aclosed+mentions%3Aethompsy)
 - [@apatao](https://github.com/apatao) | [contributions](https://github.com/pyjanitor-devs/pyjanitor/issues?q=is%3Aclosed+mentions%3Aapatao)
 - [@OdinTech3](https://github.com/OdinTech3) | [contributions](https://github.com/pyjanitor-devs/pyjanitor/pull/1094)
+- [@Fu-Jie](https://github.com/Fu-Jie) | [contributions](https://github.com/pyjanitor-devs/pyjanitor/pulls?q=is%3Aclosed+mentions%3AFu-Jie)

CHANGELOG.md

@@ -21,6 +21,7 @@
 -   [ENH] Enable `encode_categorical` handle 2 (or more ) dimensions array. PR #1153 @Zeroto521
 -   [ENH] Faster computation for a single non-equi join, with a numba engine. Issue #1102 @samukweku
 -   [INF] Cancel old workflow runs via Github Action `concurrency`. PR #1161 @Zeroto521
+-   [BUG] Modify ignore_empty output in `concatenate_columns`. PR #1164 @Fu-Jie
 
 ## [v0.23.1] - 2022-05-03
 

janitor/functions/concatenate_columns.py

@@ -51,8 +51,12 @@ 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()