Enumerable#tally

tally → new_hash

tally(hash) → hash

static VALUE
enum_tally(int argc, VALUE *argv, VALUE obj)
{
    VALUE hash;
    if (rb_check_arity(argc, 0, 1)) {
        hash = rb_to_hash_type(argv[0]);
        rb_check_frozen(hash);
    }
    else {
        hash = rb_hash_new();
    }

    return enum_hashify_into(obj, 0, 0, tally_i, hash);
}

Returns a hash containing the counts of equal elements:

Each key is an element of self.
Each value is the number elements equal to that key.

With no argument:

Example

%w[a b c b c a c b].tally # => {"a"=>2, "b"=>3, "c"=>3}

With a hash argument, that hash is used for the tally (instead of a new hash), and is returned; this may be useful for accumulating tallies across multiple enumerables:

Example

hash = {}
hash = %w[a c d b c a].tally(hash)
hash # => {"a"=>2, "c"=>2, "d"=>1, "b"=>1}
hash = %w[b a z].tally(hash)
hash # => {"a"=>3, "c"=>2, "d"=>1, "b"=>2, "z"=>1}
hash = %w[b a m].tally(hash)
hash # => {"a"=>4, "c"=>2, "d"=>1, "b"=>3, "z"=>1, "m"=> 1}

Ruby version changes

3.1
- Enumerable#tally now accepts an optional hash to count. [Feature #17744]

See also #take_while #to_a #take #to_h also in 4.1 · 4.0 · 3.4 · 3.2 · 3.1 · 3.0

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