Will REGEXP recognize specific characters within parenthesis?

Question

Brad 2017-5-9

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评论： Brad 2018-3-9

I'm attempting to use REGEXP to match a specific string within a set of parenthesis. The code I'm using is as follows;

str = '(0:20)';
exp = '([\P\0\D\d])';
tokens = regexp(str, exp, 'tokens');
b = reshape([tokens{:}], [ ], 1).';
Data = cell2mat(b);

When executed, Data contains a 1 x 6 array of char: (0:20)

I'm having difficulty in making the expression sensitive to the contents of this array. Specifically, I'm only interested in the data if the value to the left of the colon is a zero.

Is this possible when using \P as part of the expression?

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Stephen23 2017-5-10

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The MATLAB regular expression syntax is documented here:

https://www.mathworks.com/help/matlab/matlab_prog/regular-expressions.html

and it does not include any operator '\P'. In any case you have not given us any information about what data you want to obtain from the string: is it the second number value, or all of the string within parentheses, or both number values... is the colon always present, or could it be a concatenation operator instead? You state that "only interested in the data if the value to the left of the colon is a zero", but what is "the data"? Even parentheses could be data. It is only worth starting to write a regular expression once you clearly specify the requirements it has to meet.

You could start with something like this, which returns the number the follows '0:'

>> str = '(0:20)';
>> regexp(str,'(?<=0:)\d+','match','once')
ans =
20

Bonus You might like to download and try my FEX submission:

https://www.mathworks.com/matlabcentral/fileexchange/48930-interactive-regular-expression-maker

which lets you interactively develop regular expressions and see the outputs change as you type/alter your expression.

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Answer 1

Walter Roberson 2017-5-9

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MATLAB's regexp does not know anything about unicode categories. Also, \0 is not a valid unicode category name.

It looks to me as if what you are looking for is:

'\(0:\d+\)'

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Brad 2018-3-9

Walter, after looking into this more, you are correct. My search pattern was a last ditch effort to get the result that Stephen came to using his code. These regular expressions are an ongoing learning experience!!

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