Still celebrating National IT Professionals Day with 3 months of free Premium Membership. Use Code ITDAY17

x
?
Solved

regex to match exact number of occurence of a sequence

Posted on 2010-11-12
19
Medium Priority
?
853 Views
Last Modified: 2012-05-10
Hello Experts,

I try to build a regex to match an exact number of occurence of a sequence/word :

For example "abc" and the number of occurence needed "3" and only three, no more no less

So :
abcXYZabcEFGabc match
abcXYZabcEFGabcKLMabc don't match because we find four time abc
abcXYZabcEFG don't match, only two is found
abcabcabc match

I have this : /^([^a]*a[^a]*){3}$/ but it work because I'm looking for "a" and not for a sequence "ab", "JPQ"

Thanks for your help!

Kinds Regards.
0
Comment
Question by:leakim971
[X]
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
  • 8
  • 7
  • 2
  • +2
19 Comments
 
LVL 93

Assisted Solution

by:Patrick Matthews
Patrick Matthews earned 100 total points
ID: 34124152
Does it have to be RegExp?

I don't know what specific language you are using, but if you:

1) Replace "abc" with "" and

2) The resulting string is 9 characters fewer in length than the original string

then you would have a "match".
0
 
LVL 82

Author Comment

by:leakim971
ID: 34124221
Thanks a lot for your reply.
The language is Javascript and It sound stupid but I need to use a regexp.

Something like : /^([^a]*a[^a]*){3}$/.test("abcXYZabcEFGabc") will return true or false



0
 
LVL 93

Expert Comment

by:Patrick Matthews
ID: 34124293
Why must it be RegExp?
0
Industry Leaders: We Want Your Opinion!

We value your feedback.

Take our survey and automatically be enter to win anyone of the following:
Yeti Cooler, Amazon eGift Card, and Movie eGift Card!

 
LVL 1

Assisted Solution

by:phr0ze
phr0ze earned 100 total points
ID: 34124334
Try this:

(abc[a-zA-Z]*?){3}(?!.*abc)

tested at regexpal.com
0
 
LVL 14

Assisted Solution

by:sentner
sentner earned 300 total points
ID: 34124381
Can you use 2 separate regex's?  For example, this pseudocode:

if /(abc.*){3}/ then
   if /(abc.*){4}/ return false     # More than 3 matches
   else return true                      # Exactly 3 matches
else return false                        # Less than 3 matches


0
 
LVL 82

Author Comment

by:leakim971
ID: 34124429
Why a regex ? I can use it as a parameter for example.
@phr0ze and @sentner thank you I'm going to try your propositions.
0
 
LVL 75

Expert Comment

by:käµfm³d 👽
ID: 34124637
@phr0ze

The problem with your pattern is that the *? on the bracket expression will consume any trailing "abc" strings after the first three. Simply adding the negative lookahead does not overcome this.
0
 
LVL 75

Expert Comment

by:käµfm³d 👽
ID: 34124901
I believe the following satisfies the requirement:
^(?=(?:(?:[^a]|a[^ab])*abc){3}(?!.*?abc)).*$

Open in new window

0
 
LVL 82

Author Comment

by:leakim971
ID: 34124980
kaufmed this one don't match : affkaabcsjfjabckfsofabc
affk a abc sjfj abc kfsof abc

0
 
LVL 75

Expert Comment

by:käµfm³d 👽
ID: 34124988
It seems it did not upon further testing. Revised:
^(?=(?:(?:[^a]|a[^b]|a(?=a))*abc){3}(?!.*?abc)).*$

Open in new window

0
 
LVL 75

Expert Comment

by:käµfm³d 👽
ID: 34124994
Yeah, the double-a killed it. The modified version has this corrected.
0
 
LVL 82

Author Comment

by:leakim971
ID: 34125007
Don't match with : abffkabcsjfjabckfsofabc

ab ffk abc sjfj abc kfsof abc
0
 
LVL 75

Accepted Solution

by:
käµfm³d   👽 earned 1500 total points
ID: 34125071
Third time's a charm?

:)
^(?=(?:(?:a(?=a)|a[^b]|ab[^c]|[^a])*abc){3}(?!.*?abc)).*$

Open in new window

0
 
LVL 82

Author Comment

by:leakim971
ID: 34125126
@kaufmed, yes it work this time, thanks. The "problem" with this regexp is the way we build it dynamically.
The original sequence need to have three characters for example : abc

Anyway I want to thank you a lot for your time. I'm going to use an array of regex+boolean and use the logic of @sentner

I'm going to close the question
Thank you to everyone for your suggestions, have a great weekend!
0
 
LVL 82

Author Closing Comment

by:leakim971
ID: 34125198
End of week, enjoy, have a nice weekend!
Thanks a lot to everyone! Have fun in your life!
0
 
LVL 75

Expert Comment

by:käµfm³d 👽
ID: 34125279
I figured I'd throw this out there just in case, but the string shouldn't be that difficult to build dynamically; granted I don't know what your environment is like. Here is a function I created to build the pattern string:
function buildPattern(src)
{
	var basePattern = "^(?=(?:(?:@@@)*###){3}(?!.*?###)).*$";
	var temp = "";
	var t = src.charAt(0);
	
	for (i = 1; i < src.length; i++)
	{
		temp += "|" + t + "[^" + src.charAt(i) + "]";
		t += src.charAt(i);
	}

	temp = src.charAt(0) + "(?=" + src.charAt(0) + ")" + temp;
	
	return basePattern.replace(/###/g, src).replace(/@@@/, temp);
}

Open in new window

0
 
LVL 75

Expert Comment

by:käµfm³d 👽
ID: 34125286
Of course, make sure your source strings don't contain the sequences "###" or "@@@"   :)
0
 
LVL 82

Author Comment

by:leakim971
ID: 34125312
Thanks a lot @kaufmed!
0
 
LVL 75

Expert Comment

by:käµfm³d 👽
ID: 34125317
Sure. Glad to help!
0

Featured Post

Free Tool: SSL Checker

Scans your site and returns information about your SSL implementation and certificate. Helpful for debugging and validating your SSL configuration.

One of a set of tools we are providing to everyone as a way of saying thank you for being a part of the community.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

by Batuhan Cetin Regular expression is a language that we use to edit a string or retrieve sub-strings that meets specific rules from a text. A regular expression can be applied to a set of string variables. There are many RegEx engines for u…
Whatever be the reason, if you are working on web development side,  you will need day-today validation codes like email validation, date validation , IP address validation, phone validation on any of the edit page or say at the time of registration…
Learn how to match and substitute tagged data using PHP regular expressions. Demonstrated on Windows 7, but also applies to other operating systems. Demonstrated technique applies to PHP (all versions) and Firefox, but very similar techniques will w…
Explain concepts important to validation of email addresses with regular expressions. Applies to most languages/tools that uses regular expressions. Consider email address RFCs: Look at HTML5 form input element (with type=email) regex pattern: T…

721 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question