Bin Counting in Elixir: Why is Enum.group_by much faster than Enum.reduce

Questions & Help Questions
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4

Hm.. the following benchmark now shows a different result…

is_even? = fn x -> rem(x, 2) == 0 end

Benchee.run(
  %{
    "reduce" => fn range ->
      Enum.reduce(range, %{}, fn elem, acc -> Map.update(acc, is_even?.(elem), 1, &(&1 + 1)) end)
    end,
    "group" => fn range ->
      Enum.group_by(range, &is_even?.(&1)) |> Map.new(fn {key, list} -> {key, length(list)} end)
    end
  },
  inputs: %{
    "Range" => 1..1_000_000
  }
)

##### With input Range #####
Name             ips        average  deviation         median         99th %
reduce          4.65      215.08 ms    ±12.47%      209.29 ms      338.53 ms
group           2.47      405.21 ms    ±18.65%      411.79 ms      552.56 ms

Comparison:
reduce          4.65
group           2.47 - 1.88x slower +190.13 ms

So your original hunch, might be correct after all.