Given:
iex(9)> list_of_maps = [%{"a" => 1, "b" => 2, "c" => 3},%{"a" => 66, "b" => 1, "c" => 9},%{"a" => 66, "b" => 20, "c" => 8}]
I can do:
iex(10)> Enum.filter(list_of_maps, &(&1["a"] == 1))
Enum.filter(list_of_maps, &(&1["a"] == 1))
[%{"a" => 1, "b" => 2, "c" => 3}]
However now comes the part I dread writing in every language - getting the first value of this list to extract the single item.
Is there some standard function in elixir that filters a list, returning single item if there is only one item after a filter is applied, or a list of items if there are numerous items returned after the filter is applied? Like:
iex(11)> Enum.filterr(list_of_maps, &(&1["a"] == 1))
Enum.filter(list_of_maps, &(&1["a"] == 1))
%{"a" => 1, "b" => 2, "c" => 3}
iex(12)> Enum.filterr(list_of_maps, &(&1["a"] == 66))
Enum.filter(list_of_maps, &(&1["a"] == 66))
[%{"a" => 66, "b" => 1, "c" => 9},%{"a" => 66, "b" => 20, "c" => 8}]]
If you want to filter a list to get only one item, use Enum.find/2:
Enum.find(list_of_maps, fn m -> m["a"] == 1 end)
To handle both cases, pattern matching is the way to go:
defmodule MyEnum do
def filter(list, fun) do
list
|> Enum.filter(fun)
|> normalize
end
defp normalize([item]), do: item
defp normalize(list), do: list
end
You can then use it like this:
MyEnum.filter(list_of_maps, &(&1["a"] == 1))
It will return a list if there are multiple matches or the map itself if there's only one match.