Question

In Ruby, I have a string of identical characters — let’s say they’re all exclamation points, as in !!!!. I would like to replace the characters at certain indices with ‘*’ if the integer corresponding to that index meets some criteria.

For example, let’s say I want to replace all the characters whose indices are even numbers and are greater than 3. In the string !!!!!!!! (8 characters long), that results in !!!!*!*! (indices 4 and 6 have been replaced).

What’s the most compact way to do this?

Answer 1

Here is a version that will modify an existing string in place:

str = '!!!!!!!!'
str.split('').each_with_index do |ch, index|
  str[index] = '*' if index % 2 == 0 and index > 3
end