How To Get Digits Past Decimal In Elixir?

Question

This is how I'm doing it in Python... Is there a more elegant way to do it in Elixir?

def get_digits_past_decimal(number):
    number_string = str(number)
    dig_past_decimal = abs(Decimal(number_string).as_tuple().exponent)
    return dig_past_decimal

Is this accurate enough for your needs: `123.456 |> Float.to_string |> String.split(".") |> Enum.at(1) |> byte_size`? — Dogbert, Apr 16 '17 at 10:40

score 3 · Accepted Answer · edited May 23 '17 at 10:31

I'd convert the float to a string and count the number of bytes after the dot:

One Liner:

float |> Float.to_string |> String.split(".") |> Enum.at(1) |> byte_size

Slightly longer but more efficient as it doesn't create an intermediary list:

string = float |> Float.to_string
{start, _} = :binary.match(string, ".")
byte_size(string) - start - 1

Test:

defmodule A do
  def count1(float) do
    float |> Float.to_string |> String.split(".") |> Enum.at(1) |> byte_size
  end

  def count2(float) do
    string = float |> Float.to_string
    {start, _} = :binary.match(string, ".")
    byte_size(string) - start - 1
  end
end

for f <- [0.1, 0.234, 123.456, 0.0000000001] do
  IO.inspect {A.count1(f), A.count2(f)}
end

Output:

{1, 1}
{3, 3}
{3, 3}
{5, 5}

Note: the results may not be identical to Python since there are multiple ways to convert a float to a decimal string with slightly different outputs and tradeoffs. This question has some more information about this.

How To Get Digits Past Decimal In Elixir?

1 Answers1