While talking to Edward, a quick example in the ruby console came up, to remind us that if we want to replace all the occurrences in a string, we need to use gsub, and sub is not enough.

"foo,foo".sub(",", "")
=> "foofoo"

"foo,foo,foo".sub(",", "")
=> "foofoo,foo"

From the ruby docs on sub

Returns a copy of str with the first occurrence of pattern […]

So if we want to replace all the occurrences we should use gsub

Returns a copy of str with the all occurrences of pattern […]

"foo,foo,foo".gsub(",", "")
=> "foofoofoo"