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fix(rust, python): treat null columns as zero in sum_horizontal #13880

Merged
merged 6 commits into from
Jan 22, 2024
Merged

fix(rust, python): treat null columns as zero in sum_horizontal #13880

merged 6 commits into from
Jan 22, 2024

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edavisau
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Fixes #13113

  • Null columns are treated as additive identity in the presence of non-null columns. They can be skipped in the computation
  • If all columns are Null, return Null

I have also changed the behaviour of single columns sums. This seems more consistent to multi-column sums. Example:

    df = pl.DataFrame(
        {
            "A": [5, None, 3, None],
            "B": [5, 3, None, None],
        }
    )

As reference, when summing multiple columns
sum_horizontal("A", "B") = [10, 3, 3, 0]

Before
sum_horizontal("A") = [5, None, 3, None]
After
sum_horizontal("A") = [5, 0, 3, 0]

@github-actions github-actions bot added fix Bug fix python Related to Python Polars rust Related to Rust Polars labels Jan 20, 2024
stinodego
stinodego requested changes Jan 21, 2024
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Thanks for the PR!

If all columns are Null, return Null

I don't think this is correct. Null should just be treated as the identity always.

@edavisau
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@stinodego In this case I was referring to the actual Null data type, as opposed to all values being null i.e.

df = pl.DataFrame([
    pl.Series("A", [None, None, None], pl.Null),
    pl.Series("B", [None, None, None], pl.Null),
    pl.Series("C", [None, None, None], pl.Null),
])

If you replaced pl.Null with pl.Int32 above you'll get 0 in the result, similarly if you replaced with pl.Utf8 you'll get empty strings in the result. In addition, if 2 of the columns were pl.Null, and one was pl.Int32, you'd still get a pl.Int32 result. The all-pl.Null situation seemed too ambiguous though. Do you have another suggestion for this case?

Thanks!

@stinodego
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Ah, I hadn't understood that part. Then it's probably fine!

ritchie46
ritchie46 approved these changes Jan 22, 2024
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Thanks!

@ritchie46 ritchie46 merged commit 42a4231 into pola-rs:main Jan 22, 2024
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r-brink pushed a commit to r-brink/polars that referenced this pull request Jan 24, 2024
@edavisau @r-brink
fix(rust, python): treat null columns as zero in sum_horizontal (po…
fc3761d 
…la-rs#13880)
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@stinodego stinodego stinodego requested changes

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not yet implemented when call pl.sum_horizontal
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@edavisau @stinodego @ritchie46