Duplicate elements of array in ruby

Question

I find a lot of reference about removing duplicates in ruby but I cannot find how to create duplicate.

If I have an array like [1,2,3] how can I map it to an array with dubbed items? [1,1,2,2,3,3]

Is there a method?

Answer 1

Try this one

[1, 2, 3].flat_map { |i| [i, i] }
 => [1, 1, 2, 2, 3, 3] 

Answer 2

Here's yet another way, creating the array directly with Array#new :

array = [1, 2, 3]
repetitions = 2

p Array.new(array.size * repetitions) { |i| array[i / repetitions] }
# [1, 1, 2, 2, 3, 3]

According to fruity, @ursus's answer, @ilya's first two answers and mine have comparable performance. transpose.flatten is slower than any of the others.