Question

I have a string

string = '1234432198766789'

I want it to look like this:

"1234 4321 9876 6789"

What is the best way to do it? I am able to use Rails’ String extensions.

I don’t want to modify the original string, so insert method couldn’t be used.

Answer 1

p '12345678'.reverse.scan(/.{1,4}/).join(' ').reverse
# => "1234 5678"

Why the double reverse? So that when the string’s length is not a multiple of four, the odd-sized group will be on the left:

p '123456'.reverse.scan(/.{1,4}/).join(' ').reverse
# => "12 3456"

If you know your string will always be a multiple of four, or if you don’t mind the odd-sized group being on the right, then leave out the two calls to reverse.

p '123456'.scan(/.{1,4}/).join(' ')
# => "1234 56"