[erlang-questions] Case-insensitive key search on a list

Bob Ippolito <>
Mon Apr 30 20:23:38 CEST 2012


On Mon, Apr 30, 2012 at 10:54 AM, Tristan Sloughter <
> wrote:

> So you want to find a tuple in a list converted from JSON so the key is
> binary. And not only that, you want it to be case insensitive!
>
> Now as far as I found, I'm only now bothering to go back to this code and
> ask why, there is only string:equal/2 and it doesn't support case
> insensitive matching. And not only that but string:to_lower/1 only supports
> lists. So I ended up with a conversion to a list, then to_lower and then
> back to a binary....
>
> It is too ugly to think it was right... Does anyone know a better way of
> doing this? I feel I am missing something obvious.
>
> case_insensitive_binary_string_keyfind(_String, _Pos, []) ->
>     false;
> case_insensitive_binary_string_keyfind(String, Pos, [H|T]) ->
>     case list_to_binary(
>            string:to_lower(
>              binary_to_list(
>                element(Pos, H)))) of
>         String ->
>             H;
>         _ ->
>             case_insensitive_binary_string_keyfind(String, Pos, T)
>     end.
>

Well, just implement it yourself. Maybe something like this:

lower_match(<<C, B0/binary>>, <<C, B1/binary>>) ->
    lower_match(B0, B1);
lower_match(<<C0, B0/binary>>, <<C1, B1/binary>>)
  when (C1 >= $a andalso C1 =< $z andalso C0 >= $A andalso
        (C0 + ($a - $A)) =:= C1) ->
    lower_match(B0, B1);
lower_match(<<C1, B0/binary>>, <<C0, B1/binary>>)
  when (C1 >= $a andalso C1 =< $z andalso C0 >= $A andalso
        (C0 + ($a - $A)) =:= C1) ->
    lower_match(B0, B1);
lower_match(<<>>, <<>>) ->
    true;
lower_match(_B0, _B1) ->
    false.

lower_keyfind(_K, _P, []) ->
    false;
lower_keyfind(K, P, [H | T]) ->
    case lower_match(K, element(P, H)) of
        true ->
            H;
        false ->
            lower_keyfind(K, P, T)
    end.

-bob
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