Regex to replace a repeating string pattern

Question

I need to replace a repeated pattern within a word with each basic construct unit. For example I have the string "TATATATA" and I want to replace it with "TA". Also I would probably replace more than 2 repetitions to avoid replacing normal words.

I am trying to do it in Java with replaceAll method.

If you are already using replaceAll(), what is the problem? replaceAll does exactly what you want to to do (if you have a simple pattern as the one described above). — Pphoenix, Jun 03 '14 at 06:46
I don't want to replace only "TATATATA" but any string that is repeating like that. @TheLostMind I don't have any regex ideas. — Michael, Jun 03 '14 at 06:48
Do you mean any repeating characters like TATATATA or YTYTYT or ABCABCABC which may be present in a string ? — Kenneth Clark, Jun 03 '14 at 06:49
I would like to know if there is a way to match any repeating patterns. What is that thing with my code? I don't have any code this is why I am asking. — Michael, Jun 03 '14 at 06:51
Look Ahead, Look back with Regex, String#contains(), String#indexOf() etc can be used for this.. But show us your effort — TheLostMind, Jun 03 '14 at 06:51
Guys, we are talking about an one-liner probably. Either you know it or you don't. I don't see how that "show the code" is helping people. Thanks. — Michael, Jun 03 '14 at 06:52
@ddmichael: I do not think it is possible to write code that finds *any repeating pattern*. Technically all text is then a repeating pattern, only that it might just be repeated once. — Pphoenix, Jun 03 '14 at 06:56
@Pphoenix: I was afraid of that. I am looking for patterns within a word though, do you think that's possible? — Michael, Jun 03 '14 at 06:58
@ddmichael: Yes! You only have define what you see as a pattern. Example: If you have TAT, is that a pattern where every other letter is a T? Or are you looking for at least TATA? If you find a repeating pattern you would like to find, it will be possible to define code for it. — Pphoenix, Jun 03 '14 at 07:00
@Pphoenix: No I am not interested in TAT, where every other letter is a T. Ideally I would like to replace A{3,} with A, TA{3,} with TAT{3,} and so on. Hence repeating patterns of one or more continuous characters. — Michael, Jun 03 '14 at 07:07

score 9 · Accepted Answer · answered Jun 03 '14 at 07:13

I think you want this (works for any length of the repeated string):

String result = source.replaceAll("(.+)\\1+", "$1")

Or alternatively, to prioritize shorter matches:

String result = source.replaceAll("(.+?)\\1+", "$1")

It matches first a group of letters, and then it again (using back-reference within the match pattern itself). I tried it and it seems to do the trick.

Example

String source = "HEY HEY duuuuuuude what'''s up? Trololololo yeye .0.0.0";

System.out.println(source.replaceAll("(.+?)\\1+", "$1"));

// HEY dude what's up? Trolo ye .0

fge · Answer 2 · 2014-06-03T07:17:41.730

1

You had better use a Pattern here than .replaceAll(). For instance:

private static final Pattern PATTERN 
    = Pattern.compile("\\b([A-Z]{2,}?)\\1+\\b");

//...

final Matcher m = PATTERN.matcher(input);
ret = m.replaceAll("$1");

edit: example:

public static void main(final String... args)
{
    System.out.println("TATATA GHRGHRGHRGHR"
        .replaceAll("\\b([A-Za-z]{2,}?)\\1+\\b", "$1"));
}

This prints:

TA GHR

edited Jun 03 '14 at 07:17

answered Jun 03 '14 at 06:51

fge

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Didn't work, prints the whole string. Thanks for your answer! – Michael Jun 03 '14 at 07:00
Yep indeed, I was trying with an extra character at the end, like "TATATAT". – Michael Jun 03 '14 at 07:27

drew moore · Answer 3 · 2014-06-03T10:19:29.687

Since you asked for a regex solution:

(\\w)(\\w)(\\1\\2){2,};

(\w)(\w): matches every pair of consecutive word characters ((.)(.) will catch every consecutive pair of characters of any type), storing them in capturing groups 1 and 2. (\\1\\2) matches anytime the characters in those groups are repeated again immediately afterward, and {2,} matches when it repeats two or more times ({2,10} would match when it repeats more than one but less than ten times).

String s = "hello TATATATA world";    
Pattern p = Pattern.compile("(\\w)(\\w)(\\1\\2){2,}");
Matcher m = p.matcher(s);
while (m.find()) System.out.println(m.group());
    //prints "TATATATA"

I am afraid that prints only the first letter. Thanks for your answer! — Michael, Jun 03 '14 at 06:59

Regex to replace a repeating string pattern

3 Answers3

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