Description
Code Sample, a copy-pastable example if possible
df = pd.DataFrame({"key": ["a", "b", "c", "c"], "value": [1, 2, 3, 4]})
def foo(x):
print(f"called with {x}")
return len(x)
df.groupby("key")["value"].agg(foo)Problem description
In 1.0.0, this code outputs:
called with Series([], Name: value, dtype: int64)
called with 0 1
Name: value, dtype: int64
called with 1 2
Name: value, dtype: int64
called with 2 3
3 4
Name: value, dtype: int64
Out[10]:
key
a 1
b 1
c 2
Name: value, dtype: int64
In 0.25.3, the code outputs:
In [5]: df.groupby("key")["value"].agg(foo)
called with 0 1
Name: value, dtype: int64
called with 1 2
Name: value, dtype: int64
called with 2 3
3 4
Name: value, dtype: int64
Out[5]:
key
a 1
b 1
c 2
Name: value, dtype: int64
In 1.0.0, foo is called one more time with empty input, which can break user code
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Expected Output
Output of pd.show_versions()
[paste the output of pd.show_versions() here below this line]