zhengruifeng opened a new pull request, #37975:
URL: https://github.com/apache/spark/pull/37975
### What changes were proposed in this pull request?
add a new `var` expression to support arbitary integeral `ddof`
### Why are the changes needed?
for API coverage
### Does this PR introduce _any_ user-facing change?
yes, it accept `ddof` other than {0, 1}
before
```
In [1]: import pyspark.pandas as ps
In [2]: import numpy as np
In [3]: df = ps.DataFrame({'a': [1, 2, 3, np.nan], 'b': [0.1, 0.2, 0.3,
np.nan]}, columns=['a', 'b'])
In [4]: df.var(ddof=2)
---------------------------------------------------------------------------
AssertionError Traceback (most recent call last)
Cell In [4], line 1
----> 1 df.var(ddof=2)
File ~/Dev/spark/python/pyspark/pandas/generic.py:1958, in Frame.var(self,
axis, ddof, numeric_only)
1904 def var(
1905 self, axis: Optional[Axis] = None, ddof: int = 1, numeric_only:
bool = None
1906 ) -> Union[Scalar, "Series"]:
1907 """
1908 Return unbiased variance.
1909
(...)
1956 0.6666666666666666
1957 """
-> 1958 assert ddof in (0, 1)
1960 axis = validate_axis(axis)
1962 if numeric_only is None and axis == 0:
AssertionError:
```
after
```
In [4]: df.var(ddof=2)
Out[4]:
a 2.00
b 0.02
dtype: float64
In [5]: df.to_pandas().var(ddof=2)
/Users/ruifeng.zheng/Dev/spark/python/pyspark/pandas/utils.py:975:
PandasAPIOnSparkAdviceWarning: `to_pandas` loads all data into the driver's
memory. It should only be used if the resulting pandas DataFrame is expected to
be small.
warnings.warn(message, PandasAPIOnSparkAdviceWarning)
Out[5]:
a 2.00
b 0.02
dtype: float64
```
### How was this patch tested?
added UT
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