Swapping letters in a string in Ruby

Question

I need to swap letters in a string (DNA strand) using Ruby and the following rules:

• 'A' is replaced by 'T'
• 'T' is replaced by 'A'
• 'C' is replaced by 'G'
• 'G' is replaced by 'C'

For example, 'ACGTA' should become 'TGCAT'.

I have only got this far:

def DNA_strand(dna)    
  dna.tr!('A', 'T')    
end

Answer 1

You were quite close:

dna.tr('ATCG', 'TAGC')   # => "TGCAT"

See ruby-doc.org on tr:

Returns a copy of str with the characters in from_str replaced by the corresponding characters in to_str.

Use tr! the same way if you want to modify your string in-place.