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Calls the block, if given, with each element of self; returns a new Array containing those elements of self for which the block returns a truthy value:
a = [:foo, 'bar', 2, :bam]
a1 = a.select {|element| element.to_s.start_with?('b') }
a1 # => ["bar", :bam]
Returns a new Enumerator if no block given:
a = [:foo, 'bar', 2, :bam]
a.select # => #<Enumerator: [:foo, "bar", 2, :bam]:select>
Array#filter is an alias for Array#select.
 
               static VALUE
rb_ary_select(VALUE ary)
{
    VALUE result;
    long i;

    RETURN_SIZED_ENUMERATOR(ary, 0, 0, ary_enum_length);
    result = rb_ary_new2(RARRAY_LEN(ary));
    for (i = 0; i < RARRAY_LEN(ary); i++) {
        if (RTEST(rb_yield(RARRAY_AREF(ary, i)))) {
            rb_ary_push(result, rb_ary_elt(ary, i));
        }
    }
    return result;
}
            

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