Using Ruby regex gsub only once

Question

I have the following string.

melody = "F# G# A# B |A# G# F#   |A# B C# D# |C# B A#   |F#   F#   
         |F#   F#   |F#F#G#G#A#A#BB|A# G# F#   "

I want to convert F# to f, G# to g etc.

melody.gsub(/C#/, 'c').gsub(/D#/,'d').gsub(/F#/,'f').gsub(/G#/,'g').gsub(/A#/,'a')

The above gives a desired output. But I am wondering if I can use gsub only once.

"f g a B |a g f   |a B c d |c B a   |f   f   |f   f   |ffggaaBB|a g f   "

falsetru · Accepted Answer · 2014-06-07 05:59:43Z

4

String#gsub accepts an optional block: return value of the block is used as replacement string:

melody.gsub(/[CDFGA]#/) { |x| x[0].downcase }
# => "f g a B |a g f   |a B c d |c B a   |f   f   |f   f   |ffggaaBB|a g f   "

answered Jun 7, 2014 at 5:59

falsetru

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7 Comments

do lowercase conversion..while substituting.

Short and sweet! +1 :)

Can you do this without a block, using a back reference?

@CarySwoveland, No, I can't.

@CarySwoveland Here is the answer, why not possible...

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user1375096 · Accepted Answer · 2014-06-07 06:21:31Z

1

You can use hash too.

melody.gsub(/[CDFGA]#/, {'C#' => 'c', 'D#' => 'd', 'F#' => 'f', 'G#' => 'g', 'A#' => 'a'})

answered Jun 7, 2014 at 6:21

user1375096

I don't think this is the most efficient solution in this case, but it is useful for you to have shown how to do more general substitutions.

yes, it's not short, but more general if your substitution has no relation with the matching.