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

September 9, 2025

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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}

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