Comments (5)
You can do that with a when -> then -> otherwise
:
foo = pl.col("foo")
pl.when(foo.is_null()).then(foo.mode().first())
And fill_null
also accepts expressions:
foo.fill_null(foo.mode().first())
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What if there is not a unique mode?
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This is a good point. https://docs.pola.rs/py-polars/html/reference/series/api/polars.Series.mode.html do mention the possibility of having multiples values. I guess this would involve having a method to tie break them which could be none or random for example. This will then be a feature request for mode.
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Thanks @ritchie46, I was not mentioning it is not possible. I actually use the fill_null
that you mentioned in your example but I was referring that it could be good to either add this example in the doc or as a strategy
option for the method arguments in https://github.com/pola-rs/polars/blob/py-0.20.30/py-polars/polars/dataframe/frame.py#L7202 as this is pretty helpful for string and the other alternatives ({None, ‘forward’, ‘backward’, ‘min’, ‘max’, ‘mean’, ‘zero’, ‘one’}
) do not help in the case of string.
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Someone did request this previously #15007 but they closed the issue.
(So it seems like a useful doc example at the very least?)
.mode()
does counts nulls
>>> pl.Series([1, None]).mode()
shape: (2,)
Series: '' [i64]
[
1
null
]
>>> pl.Series([1, None, None]).mode()
shape: (1,)
Series: '' [i64]
[
null
]
I've not seen it mentioned before, so I'm not sure if this is intended or not - but currently you'd need to drop them.
For comparison, pandas drops them by default:
>>> pd.Series([1, None, None]).mode()
0 1.0
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