regexp pattern for only allowing numbers at the end of a string?

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Wolf
Wolf 2018-1-20
回答： Anushka 2025-1-31
I have a cell array of strings and need to figure out which strings match a certain pattern.
Rules for when the pattern should match
1. The string contains integers separated by '-'
2. The string has to start with '2' or '3'
3. The string has to end with '6'
4. The string has to end with an arbitrary repetition of '-5' (including 0 times)
5. After the first occurence of '-5' no other numbers except the final 6 (see rule 3) are allowed (e.g. not allowed: 3-1-5-1-5-6)
Examples where the regexp pattern should match:
3-5-5-5-5-6
3-6
3-1-2-1-2-2-5-5-5-6
3-1-2-5-6
Examples where the regexp pattern should not match:
3-1-5-1-5-6
3-1-5-1-5-5-5-6
My question: Which regexp pattern realizes rules 1-4?
I've already managed to find a regext pattern that checks against rules 1-4 in the list above. However, I don't know how to add rule 5 to the pattern:
% Create patternDirectRays = a regexp pattern for the direct rays
% Example: The regexp pattern <pattern> for start numbers 2 and 3, last-but-one-numbers 5 and last number 6 is
% pattern = '^(2|3)(-5)*(-6)$' => ^(2|3) means 'has to start with 2 or 3' / (-5)* means ...followed by 0,1 or more repetitions of '-5' / (-6) = ..and finishes with '-6'
% The following strings would match <pattern>:
% regexp('3-5-5-6', '^(2|3)(-5)*(-6)$', 'match') => '3-5-5-6'
% regexp('2-5-5-6', '^(2|3)(-5)*(-6)$', 'match') => '3-5-5-6'
% regexp('3-5-5-5-5-6', '^(2|3)(-5)*(-6)$', 'match') => '3-5-5-5-5-6'
% regexp('3-6', '^(2|3)(-5)*(-6)$', 'match') => '3-6'
myPattern = '^(2|3)(-5)*(-6)$'
% Get indices of matching strings
idx = regexp(rayPaths, myPattern, 'start');

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回答（1 个）

Anushka
Anushka 2025-1-31
Hello @Wolf,
To include Rule 5 in your regular expression pattern, you need to ensure that after the first occurrence of -5, no other numbers except the final -6 are allowed. Follow the below mentioned steps to construct the pattern :
1. Start with 2 or 3.
2. Allow any sequence of numbers and dashes, but after the first occurence of -5 , only -5 or -6 can follow.
3. Ensure the string ends with -6.
Here's the updated regular expression pattern:
myPattern = '^(2|3)(-[0-9]+)*(-5)*-6$';
For applying the pattern, 'regexp' function can be utilized.
Refer to the below mentioned MATLAB Documentation link for the ‘regexp’ function:
https://www.mathworks.com/help/matlab/ref/regexp.html
Hope this helps.

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