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mirror Map.filter/2 perf note in Map.reject/2 #15373

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josevalim merged 1 commit into from
May 13, 2026
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mirror Map.filter/2 perf note in Map.reject/2 #15373

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13 changes: 10 additions & 3 deletions lib/elixir/lib/map.ex
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Expand Up @@ -1138,9 +1138,9 @@ defmodule Map do
> #### Performance considerations {: .tip}
>
> If you find yourself doing multiple calls to `Map.filter/2`
> and `Map.reject/2` in a pipeline, it is likely more efficient
> to use `Enum.map/2` and `Enum.filter/2` instead and convert to
> a map at the end using `Map.new/1`.
> and/or `Map.reject/2` in a pipeline, it is likely more efficient
> to use `Enum.filter/2` and `Enum.reject/2` instead and convert to
> a map at the end using `Map.new/1` or `Map.new/2`.

## Examples

Expand Down Expand Up @@ -1172,6 +1172,13 @@ defmodule Map do

See also `filter/2`.

> #### Performance considerations {: .tip}
>
> If you find yourself doing multiple calls to `Map.filter/2`
> and/or `Map.reject/2` in a pipeline, it is likely more efficient
> to use `Enum.filter/2` and `Enum.reject/2` instead and convert to
> a map at the end using `Map.new/1` or `Map.new/2`.

## Examples

iex> Map.reject(%{one: 1, two: 2, three: 3}, fn {_key, val} -> rem(val, 2) == 1 end)
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