[ENH] Fix check_column to support single inputs (#811)

* fix check_column to support single inputs; change sklearn dep to scikit-learn

* add entry to changelog and fix dupe changelog entry

Author: zbarry

.requirements/base.in

@@ -4,5 +4,5 @@
 natsort
 # seaborn
 pandas_flavor
-sklearn
+scikit-learn
 multipledispatch

CHANGELOG.md

@@ -4,9 +4,7 @@
 
 - [ENH] Add `dropna` parameter to groupby_agg. @samukweku
 - [ENH] `complete` adds a `by` parameter to expose explicit missing values per group, via groupby. @samukweku
-
-- [ENH] Add `dropna` parameter to groupby_agg. @samukweku
-- [ENH] `complete` adds a `by` parameter to expose explicit missing values per group, via groupby. @samukweku
+- [ENH] Fix check_column to support single inputs - fixes `label_encode`. @zbarry
 
 ## [v0.20.13] - 2021-02-25
 

janitor/utils.py

@@ -42,7 +42,7 @@ def check(varname: str, value, expected_types: list):
 
         check('x', x, [int, float])
 
-    :param varname: The name of the variable.
+    :param varname: The name of the variable (for diagnostic error message).
     :param value: The value of the varname.
     :param expected_types: The types we expect the item to be.
     :raises TypeError: if data is not the expected type.
@@ -360,6 +360,9 @@ def check_column(
         in df.columns.
     :raises ValueError: if data is not the expected type.
     """
+    if isinstance(column_names, str) or not isinstance(column_names, Iterable):
+        column_names = [column_names]
+
     for column_name in column_names:
         if present and column_name not in df.columns:  # skipcq: PYL-R1720
             raise ValueError(

tests/utils/test_check_column.py

@@ -11,6 +11,27 @@ def test_check_column(dataframe):
     assert check_column(dataframe, ["a"]) is None
 
 
+@pytest.mark.utils
+def test_check_column_single(dataframe):
+    """
+    Check works with a single input
+    """
+
+    assert check_column(dataframe, "a") is None
+
+    with pytest.raises(ValueError):
+        check_column(dataframe, "b")
+
+    # should also work with non-string inputs
+
+    with pytest.raises(ValueError):
+        check_column(dataframe, 2)
+
+    dataframe[2] = "asdf"
+
+    assert check_column(dataframe, 2) is None
+
+
 @pytest.mark.utils
 def test_check_column_absent_column(dataframe):
     """