How can we efficiently count the digits in an integer in Elixir?

Question

How can we efficiently count the digits in an integer in Elixir?

My attempt in Iex

iex(1)> a=100_000                                               
100000
iex(2)> Enum.reduce(1..a, &(&1*&2))|> to_string|> String.length
456574
iex(3)> 

Takes over 15 seconds

Another Implementation:

defmodule Demo do
    def cnt(n), do: _cnt(n,0)
    defp _cnt(0,a), do: a
    defp _cnt(n,a),do: _cnt(div(n,10),a+1)
end

Is way slower: b = 100_000!

A suggestion from the comments (Thanks Fred!)

iex> Integer.to_char_list(b) |> length

Is best so far and simplest

IEx> :timer.tc(fn -> Demo.cnt b  end)
{277662000, 456574}
IEx> :timer.tc(fn ->b |> to_string |> String.length end) 
{29170000, 456574}

Is there built in wizardry for this in any Elixir module?

Answer 1

From Elixir 1.1 and above there is now a built in feature

Integer.digits/2

This effectively handles digit counting