Question

How can I randomly replace substring, exactly n-times in Ruby?

For example, I have a text:

foo foo foo foo bar bar foo bar foo bar

I want to replace two random foos with boo in any part of string above.

These are the possible results:

1. foo foo boo foo bar bar foo bar boo bar
2. boo foo foo foo bar bar boo bar foo bar
3. foo boo foo boo bar bar foo bar foo bar
4. etc..

Answer 1

str = "foo foo foo foo bar bar foo bar foo bar"
num = 2
# get an array of all foo's; replace 2 foos with boo; shuffle the array.
ar = (["boo"]*num + str.scan(/foo/)[num..-1]).shuffle
# replace each foo with the next element of the array.
str.gsub(/foo/){ ar.pop }