[Proposal] Add String.count/2

[Steffen Deusch]

Hello everyone,

I recently came across the need to count all the occurrences of a pattern inside a String. First, I used `String.split(string, pattern)` and then counted the number of parts (-1). Then it was suggested to me to use `:binary.matches` instead and simply count the number of entries. This is quite straightforward, but you need to know about `:binary.matches`, so I wondered if the Elixir `String` module should include something like `String.count/2` instead:

@doc ~S"""

Counts the number of occurrences of a pattern in a string.

## Examples

iex> String.count("hello world", "o")

2

iex> String.count("hello world", "l")

3

iex> String.count("hello world", "x")

0

"""

@spec count(t, pattern) :: non_neg_integer

@doc since: "1.19.0"

def count(string, pattern) do

Enum.count(:binary.matches(string, pattern))

end

As you can see, the implementation is quite straightforward, so I'm not sure if it's worth to be included. Let me know what you think!

Happy to send a PR.

[Roman Smirnov]

Interesting. I didn't know about :binary.matches/2

I usually use that way to solve the original task:

Regex.scan(pattern, string) |> Enum.count

But I guess would be nice to have a helper for it. Maybe not `count` (could be ambiguous, b/c it's a synonym of length), maybe substr_count

четверг, 17 апреля 2025 г. в 14:48:11 UTC+3, steffen...@dashbit.co:

[José Valim]

For consistency, our version of String.count should also accept regexes as patterns, as supported in String.replace and others.

José Valim

https://dashbit.co/

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