Finding patterns in numbers while parsing Ruby

Question

If I have a list of numbers like
112536
523534
241255
233345
212121
in a text file.

And I want to find any number where a digit is repeated three times in a row or a 2-digit set is repeated three times in a row, how would I do that?

The dumb way to do it is something like

while (line = f.gets)
   g.puts line if line =~ /111/
   g.puts line if line =~ /222/
   g.puts line if line =~ /333/  
   etc...

But that's obviously not efficient. Is there a simpler way to do this?

Bart Kiers · Accepted Answer · 2011-09-07 19:35:15Z

5

Try the pattern:

(\d)\1\1

which repeats a single digit 3 times and:

(\d\d)\1\1

will repeat two digits 3 times. Combining them would look like:

(\d\d?)\1\1

The parenthesis around the \d\d? will save that single- or double digit in match group 1, and then that group is repeated twice (\1\1).

answered Sep 7, 2011 at 19:11

Bart Kiers

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5 Comments

Great, thanks! From that, I already figured out the second example, which is (\d\d)\1\1

You forgot the |(\d\d)\2\2 part.

And if I want to find 223322, I can with (\d)\1(\d)\2(\d)\1

@mu, ah, yeah, missed that part. Thanks. I shortened it a little though: (\d\d?)\1\1

@Magnus, yeah you seem to get the hang of it. Good!