Add isna (#76)

Author: jrbourbeau

dask_expr/expr.py

@@ -366,6 +366,9 @@ def count(self, numeric_only=None):
     def astype(self, dtypes):
         return AsType(self, dtypes)
 
+    def isna(self):
+        return IsNa(self)
+
     def apply(self, function, *args, **kwargs):
         return Apply(self, function, args, kwargs)
 
@@ -731,6 +734,11 @@ class AsType(Elemwise):
     operation = M.astype
 
 
+class IsNa(Elemwise):
+    _parameters = ["frame"]
+    operation = M.isna
+
+
 class Apply(Elemwise):
     """A good example of writing a less-trivial blockwise operation"""
 

dask_expr/tests/test_collection.py

@@ -124,6 +124,8 @@ def test_conditionals(func, pdf, df):
         lambda df: df.apply(lambda row, x, y=10: row * x + y, x=2),
         lambda df: df[df.x > 5],
         lambda df: df.assign(a=df.x + df.y, b=df.x - df.y),
+        lambda df: df.isna(),
+        lambda df: df.x.isna(),
     ],
 )
 def test_blockwise(func, pdf, df):