# Why are missing values not ignored by default?

**URL:** https://discourse.julialang.org/t/why-are-missing-values-not-ignored-by-default/106756
**Category:** Internals & Design
**Tags:** data, missing-values
**Created:** [November 26, 2023, 1:45am UTC](https://discourse.julialang.org/t/why-are-missing-values-not-ignored-by-default/106756 "2023-11-26T01:45:36Z")
**Posts on this page:** 1
**Showing post:** 106

<div class="post-metadata">

### Author: ![adienes](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/adienes/32/37459_2.png) [@adienes](https://discourse.julialang.org/u/adienes)
#### Post date: [November 28, 2023, 3:35pm UTC](https://discourse.julialang.org/t/why-are-missing-values-not-ignored-by-default/106756/106 "2023-11-28T15:35:32Z")

</div>

in polars:

```julia
df.select(pl.corr(col1, col2))

```

vs in Julia you have to write your own

```julia
function missing_cor(a,b)
    mask = (!).(ismissing.(a) .|| ismissing.(b))
    cor(a[mask], b[mask])
end

combine(df, [:col1, :col2] => missing_cor)

```

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