Add callable filters to isin selector (#16)

CHANGELOG.rst

@@ -3,6 +3,8 @@
 Changelog
 =========
 
+* :func:`~selectors.isin` accepts callable filters :pull:`16`, f.ex.
+  ``df.loc[isin(year=lambda s: s>2000)]``
 * New function :func:`~core.concat` makes concatenation level aware :pull:`14`
 
 v0.2.5 (2023-05-04)

src/pandas_indexing/selectors.py

@@ -84,8 +84,12 @@ def __call__(self, df):
         if self.ignore_missing_levels:
             filters = {k: v for k, v in filters.items() if k in index.names}
 
-        tests = (index.isin(np.atleast_1d(v), level=k) for k, v in filters.items())
-        return reduce(and_, tests)
+        def apply_filter(value, level):
+            if callable(value):
+                return value(index.get_level_values(level))
+            return index.isin(np.atleast_1d(value), level=level)
+
+        return reduce(and_, (apply_filter(v, k) for k, v in filters.items()))
 
 
 def isin(
@@ -101,6 +105,7 @@ def isin(
         If set, levels missing in data index will be ignored
     **filters
         Filter to apply on given levels (lists are ``or`` ed, levels are ``and`` ed)
+        Callables are evaluated on the index level values.
 
     Returns
     -------

tests/test_selectors.py

@@ -17,6 +17,9 @@ def test_isin_mseries(mseries: Series):
     sel = isin(num=[2, 3], str="foo")
     assert_series_equal(mseries.loc[sel], mseries.iloc[[1]])
 
+    sel = isin(num=lambda s: s > 1)
+    assert_series_equal(mseries.loc[sel], mseries.iloc[[1, 2]])
+
 
 def test_isin_ignore_missing_levels(mseries: Series):
     sel = isin(str="foo", bla=False)