Here is a simpler version with Map.update:
Enum.reduce items, %{}, fn item, map ->
Map.update(map, item, 1, & &1 + 1)
end
To be quite honest, I don't think this particular case is important enough
to warrant its own function. :)
Thank you David!
*José Valim*
www.plataformatec.com.br
Skype: jv.ptec
Founder and Director of R&D
On Tue, May 3, 2016 at 9:00 AM, David Whitlock <[email protected]>
wrote:
> Hi all,
>
> In many languages, there is a multiset functionality (in Python, this is
> called Counter), which produces a map with the counts of each item from a
> list. For example, you might want to do a word search of a text stream, and
> after converting the text to a list of words, you can then call the
> multiset / counter function and it would produce something like this:
>
> %{"the" => 34, "cat" => 2, "mat" => 7}
>
> I've found this functionality very useful in the past, and I was wondering
> if it might be added to the standard library.
>
> My proposal is to add something like the following function to the Enum
> module:
>
> def counter(items) do
> Enum.reduce items, %{}, fn key, map ->
> current = case :maps.find(key, map) do
> {:ok, value} -> value
> :error -> 0
> end
> :maps.put(key, current + 1, map)
> end
> end
>
> This would take any list and return a map containing the 'counts' of each
> item. I don't see the need for creating a separate multiset type. It can
> just be used like any other map.
>
> Please let me know what you think,
> David
>
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