Remove a comma from string in Ruby then cast to integer

Question

Weird observation here:

2.0.0-p353 :016 > "1,056".gsub!(/,/,'').to_i
 => 1056 
2.0.0-p353 :017 > "955".gsub!(/,/,'').to_i
 => 0

Is there a way to consistently do this without breaking numbers that do not field a , in them?

gsub!, like many other bang methods, returns nil if no change is made. — Cary Swoveland
– Cary Swoveland, Commented Jun 9, 2015 at 22:11
Why would you want to mutate the string before converting it to an integer? — Cary Swoveland
– Cary Swoveland, Commented Jun 9, 2015 at 22:16
@randombits just "955".gsub(/,/,'').to_i (no exclamation mark) works fine, that's Cary's point — steenslag
– steenslag, Commented Jun 9, 2015 at 22:24
Thanks for the greenie, but you really should hold off awhile, so as to not discourage other answers (which could be quite interesting). Feel free to withdraw the checkmark if you like. — Cary Swoveland
– Cary Swoveland, Commented Jun 9, 2015 at 22:50

Cary Swoveland · Accepted Answer · 2015-06-10 02:11:08Z

1

I assumed the requirement was:

the receiver is a string held by a variable (as there is no point in mutating the receiver if it's a string literal);
commas, if present, are to be removed from the receiver (i.e., the receiver is to be mutated); and
the receiver is to be converted to an integer and the integer returned.

One way to do that is as follows:

str = "955"
str.tap { |s| s.delete!(',') }.to_i
  #=> 955
str
  #=> "955" 

str = "1,955"
str.tap { |s| s.delete!(',') }.to_i
  #=> 1955
str
  #=> "1955"

str = "1,955,658"
str.tap { |s| s.delete!(',') }.to_i
  #=> 1955658 
str
  #=> "1955658"

edited Jun 10, 2015 at 2:11

answered Jun 9, 2015 at 22:23

Cary Swoveland

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2 Comments

the Tin Man Over a year ago

Don't use split(',').join. Instead use delete(',').to_i. It's over 2x times faster.

Cary Swoveland Over a year ago

randombits, I agree with @theTinMan completely (but not because of the benchmark results). I suggest you move the checkmark to his answer. My initial answer mutated the string to remove commas and return the integer value. I thought that was what you specifically wanted. I played around with other methods and somehow half-forget the requirement to mutate the string. :-) split(',').join is neither fish nor foul: it doesn't mutate the receiver and it's inferior to delete if the receiver is not to be mutated. I'll revert to my original answer, slightly improved.

the Tin Man · Accepted Answer · 2015-06-09 23:09:03Z

Sigh... benchmarks people...

require 'fruity'

NUM = '1,234,567,890'

compare do 
  _delete { NUM.delete(',').to_i }
  _gsub { NUM.gsub(',', '').to_i }
  _scan {NUM.scan(/\d+/).join.to_i }
  _split { NUM.split(',').join.to_i }
end
# >> Running each test 4096 times. Test will take about 1 second.
# >> _delete is faster than _split by 2.4x ± 0.1
# >> _split is faster than _gsub by 10.000000000000009% ± 1.0%
# >> _gsub is faster than _scan by 2.2x ± 0.1

In other words, use delete(',') to remove the delimiting commas and then convert the resulting string to an integer. Don't split it into an array and then rejoin it, don't scan it into an array, and don't let gsub convert ',' into a regex and then replace all matches with ''.

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