Count the number of non-numeric characters in a string and then sum their values

if !is_numeric?(char) do
  Map.update(acc, char, 1, &(&1 + 1))
else
  acc
end

Hi @LostKobrakai

Map.update/4

Thanks so much!

Just be aware of the fact that is_numeric? is an unidiomatic name for a function, either we use the prefix is_ when we have guardsave predicates or we use the suffix ? when the predicate is not guardsafe.

Hi @NobbZ
Thank you for your clarification.
So the proper name would be:

def numeric?(char) do
    Regex.match?(~r/^\d+$/, char)
end

Correct?

Since you’re summing them up at the end, I guess you don’t really need to keep the frequency map - you can just keep the sum (unless you also output the map somewhere).

With that in mind, this is how I’d write it:

def total_non_numeric_chars(string), do: loop(string, 0)

defp loop(<<char, rest::binary>>, count) when char in ?0..?9, do: loop(rest, count)
defp loop(<<_, rest::binary>>, count), do: loop(rest, count + 1)
defp loop(<<>>, count), do: count

Caveat:

iex(1)> String.codepoints "noe\u0308l"
["n", "o", "e", "̈", "l"]
iex(2)> String.graphemes "noe\u0308l"
["n", "o", "ë", "l"]
iex(3)> 

Hi @michalmuskala
This is a very interesting approach.
Thanks so much for sharing it.

I just thought of using the new reduce comprehensions. With that it can be a one-liner:

for << <<char>> <- string >>, char not in ?0..?9, reduce: 0, do: (acc -> acc + 1)

Hello @peerreynders.
Thank you very much for pointing this caveat.

That is very impressive.

Could you share a link that can take me to the “new reduce comprehensions” documentation?

Thank you very much