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30 lines
803 B
Markdown
30 lines
803 B
Markdown
# Remove One List From Another
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The `--/2` operator allows you to subtract two lists, that is, remove all
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elements in the _right_ list from the _left_ list. Each occurrence of an
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element is removed if there is a corresponding element. If there is no
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corresponding element, it is ignored.
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Here are some examples.
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```elixir
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> [1, 2, 3] -- [2, 4]
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[1, 3]
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> [:a, :b, :c, :a, :d, :a] -- [:a, :a]
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[:b, :c, :d, :a]
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```
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This kind of list operation is not particularly efficient, so for large
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lists it can be quite slow. The following example took several minutes to
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run.
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```elixir
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> Enum.into(1..1000000, []) -- Enum.into(2..1000000, [])
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[1]
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```
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To achieve a true set difference, you'll note that the docs for this
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operator recommend checking out `MapSet.difference/2`.
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See `h Kernel.--` for more details.
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