[FEATURE] Add partition

[Chalarangelo]

Description

Lodash #100 -> https://lodash.com/docs/4.17.4#partition

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Types of changes

• Bug fix (non-breaking change which fixes an issue)
• Enhancement (non-breaking improvement of a snippet)
• New feature (non-breaking change which adds functionality)
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Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have checked that the changes are working properly
• I have checked that there isn't any PR doing the same
• I have read the CONTRIBUTING document.

[atomiks]

I believe using parens + comma operator can make it one line.

const partition = (arr, fn) =>
  arr.reduce((acc, val, i, arr) => (acc[fn(val, i, arr) ? 0 : 1].push(val), acc), [[],[]]);

[Chalarangelo]

@atomiks I thought about it when I was writing the snippet, it looks slightly confusing like that, I feel. Plus we have a few snippets with the same kind of style, so I decided to go with that style for consistency.

[atomiks]

@Chalarangelo see the edit- you can also stick the ternary inside the acc[], which makes it shorter. You can also use concat here, no?

nvm concat can't be used since it relies on mutating the inner arrays

[Chalarangelo]

Array.concat() is terriby slow, so we avoid using it for such cases in general. Sticking the ternary inside the [] is not a bad idea, however the comma operator next to that will just be a bit too much and the rest of the snippets don't use it anyways, so I guess just the ternary should be enough of an improvement.

[skatcat31]

Reduce is a weird monster, but this works as advertised. To only awkward part is needing the parens, which harms readability but not enough to not consider it

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