How to group and count occurrences of values in Elixir's list

If you ever had to count occurrences of values in Elixir's list, this short post might be helpful for you!

Let's assume that the input contains a list of people names:

people = [
  %{name: "John"},
  %{name: "Tom"},
  %{name: "John"},
  %{name: "David"}
]

Our goal here is to count occurrences of names so that in the end we'll get this summary:

%{"David" => 1, "John" => 2, "Tom" => 1}

In Elixir, it's super easy! You can use Enum.frequencies_by/2 to achieve that in a simple one-liner:

iex > Enum.frequencies_by(people, & &1.name)
%{"David" => 1, "John" => 2, "Tom" => 1}