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I've been trying to build a pattern in Java to split the following string by dashes AND by tab characters. The exception is that if a dash appears after a tab has already been encountered in the string, even once, we stop splitting on the dash and only split on tabs. For example:

Input string (those big spaces are tab characters):

"4852174--r-watch   7   47  2   0   80-B    20  5"

Expected output: ["4852174", "r", "watch", "7", "47", "2", "0", "80-B", "20", "5"]

I'm using the following regular expression so far: "(?<!\\d)(\\-+)(?!\t)|\t"

The first set of brackets to signal I don't want any numbers preceding the delimiter, the next to signal that I want one or more dashes, and the last set to note that I want no tabs to follow. Of course, the OR at the end is for splitting by single tab characters.

The result that I'm getting is the following: ["4852174-", "r", "watch", "7", "47", "2", "0", "80-B", "20", "5"]

Notice the extra dash in the "4852174-" that should not be there. I've tried for very long to try to figure this out but any small change I make ruins the splitting elsewhere.

Any help to solve this problem would be much appreciated. Thank you in advance!

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  • just to clarify, my knowledge regarding regex is not that good however this might be useful to someone. Sir do you want to split it from one or more dashes ? if so why do you except 80-B as an output ? Commented Nov 19, 2013 at 10:28
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    The remaining dash is preceded by a digit, so it won't get matched (the (?<!\d) part of your regex). It seems to me that you're missing some rules that you would need. Could you answer: why should 80-B not be splitted? Commented Nov 19, 2013 at 10:28
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    @Manbearpig: There is no tab after dash in 80-B so why should that not split? Commented Nov 19, 2013 at 10:38
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    Check (?:[^\s-]|(?<=\d)-(?=[^\W\d]))+. I thought about matching instead of splitting. I think that your rules aren't well defined so I just made it "work" for the input you've provided. Commented Nov 19, 2013 at 10:39
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    OP here. My rules, as you guys noticed, were incorrect. I've since updated them in case someone else encounters this question in the future and is looking for a solution. I've been trying to use .split() and it wasn't working for any solution presented so far but using @HamZa's regular expression with pattern/matcher, it works! Thanks. Commented Nov 20, 2013 at 4:08

2 Answers 2

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The regex

\t|-+(?!\w\t)

will split the string into your desired array, but without further clarification what you want to do I can not tell you if it will work for other Strings.

You can test regex at www.regexpal.com (This is with your regex.)

Please note that you have to escape the backslash in Java. So in Java it will be

\\t|-+(?!\\w\\t)
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2 Comments

It will also not split A-B\t not sure if OP meant this.
This worked, using .split()! Thank you a whole bunch.
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The regex for matching your string is: ^(([^-\s]+?)[-\s]*)+$

The above regex will match your string even if hyphens(-) are repeated more than twice. You can get the expected output by obtaining matches from group 2 (\2).

group 1 matching: (([^-\s]+?)[-\s]*)

group 2 matching: ([^-\s]+?) => this is the grouping you will need for constructing your output.

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Thanks for replying! I tried ^(([^-\s]+?)[-\s]*)+$ using pattern/matcher and it didn't work for the dashes. Nor for .split().

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