Best way to split arrays into multiple small arrays in ruby

You're looking for Enumerable#partition:

x = [1, 2, 3, "a", "b", 4]numbers, not_numbers = x.partition{|item| item.kind_of?(Fixnum)}# => [[1, 2, 3, 4], ["a", "b"]]

Just to throw some more solutions into the pool:

x = [1,2,3,"a","b",4]numbers = x.select{ |e| e.is_a?(Fixnum) } # => [1, 2, 3, 4]letters = x - numbers # => ["a", "b"]numbers = x.select{ |e| e.kind_of?(Fixnum) } # => [1, 2, 3, 4]letters = x - numbers # => ["a", "b"]

or

(numbers, letters) = x.group_by {|a| a.class}.values_at(Fixnum, String)numbers # => [1, 2, 3, 4]letters # => ["a", "b"]

Along with some benchmarks showing how a subtle change effects speed:

require 'benchmark'x = [1,2,3,"a","b",4] * 100n = 10_000Benchmark.bm do |bench|  bench.report { n.times {    numbers = x.select{ |e| e.is_a?(Fixnum) }    letters = x - numbers  }}  bench.report { n.times {    numbers = x.select{ |e| e.kind_of?(Fixnum) }    letters = x - numbers  }}  bench.report { n.times {    (numbers, letters) = x.group_by {|a| a.class}.values_at(Fixnum, String)  }}  bench.report { n.times {    numbers, not_numbers = x.partition{|item| item.kind_of? Fixnum}  }}end# >>       user     system      total        real# >>   4.270000   0.010000   4.280000 (  4.282922)# >>   4.290000   0.000000   4.290000 (  4.288720)# >>   5.160000   0.010000   5.170000 (  5.163695)# >>   3.720000   0.000000   3.720000 (  3.721459)

Try:

x.group_by {|x| x.class}

You can get an array back by then calling to_a on the result which in the example you've given will return:

[[Fixnum, [1, 2, 3, 4]], [String, ["a", "b"]]]