docs: Correct the definition of an expression in the user guide #14750
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fn(Series) -> Series to fn(DataFrame) -> Series)
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I hope it's OK to suggest this change - it's been bugging me for a bit, and trying to translate the Polars API to the pandas API I kept coming up against this
If we consider the expression
expr = pl.sum_horizontal('a', 'b').abs(), then it roughly translates toSo the input is a dataframe, not a series. The output is always a Series, which is why you can keep chaining expressions - they just keep acting on the output Series from the previous step
EDIT: I think I also heard Orson describe expressions in these terms, but can't find the message now