unexpected comma in regexp output

Hi, everyone, I want to extract the word "Df(3R)ED50003". from a string below:

The word is composed of A-Z a-z 0-9 - _ ( )

aStr = 'w[1118]; Df(3R)ED50003, P{w[+mW.Scer\FRT.hs3]=3''.RS5+3.3''}ED50003/TM6C, cu[1] Sb[1]';

Below is the code I used:

[t1,t2] = regexp(aStr,'.*(Df[\(\)-_a-zA-Z0-9]+).*','tokens')

However, I got :

t1{1}{1}
    Df(3R)ED50003,

There is a comma in the end which I did not include in the regexp. I expect Df(3R)ED50003, but the results has one more comma.

Can someone help me on where an I wrong? Thanks

Answer 1

[Guillaume]

Note your example input is not valid matlab syntax. I assume the internal ' are meant to be doubled.

I'm not too sure what you're trying to do with your regex, some of it is overcomplicated, e.g.:

regexp(s, '.*(somexepr).*', 'tokens')

is the same as the simpler (and most likely much faster, .* can slow regexp tremendously if used carelessly)

regexp(s, 'somexpr', 'match')

I'm not entirely clear on what exactly you want to include in your match. I don't think you understand fully how [] works in a regexp, and in particular the role of - in there. Your [\(\)-_a-zA-Z0-1]+ expression matches one or more of:

• a (, your \(,
• any character in the range '(':'_', your \)-_, note that this range does include the comma. It's probably where you went wrong.
• any character in the range 'a':'z',
• any character in the range 'A':'Z',
• 0, or 1, which you have written as 0-1 but could be written more simply as 01

>> '(':'_'  %all characters matched by \)-_
ans =
    '()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_'

[raym]

Thanks.I'm wrong at not add a slash \ before - to indicate the char - itself.

Below works:

'.*(Df[\(\)\-_a-zA-Z0-9]+).*'

[Guillaume]

Or you could move the - to the beginning or the end of the list, where it doesn't need escaping:

'[-\(\)_a-zA-Z0-9]+' % - doesn't need escaping when it's the first in the list
%or
'[\(\)_a-zA-Z0-9-]+' % or when it's the last

[raym]

Yes.

I also found that below two command is same:

regexp(s, 'somexpr', 'match')
regexp(s, '(somexpr)', 'match')

somexpr can be surround by () even when there is no () in string.

[Stephen23]

"somexpr can be surround by () even when there is no () in string."

That is because parentheses are a grouping operator, not literal characters:

https://www.mathworks.com/help/matlab/matlab_prog/regular-expressions.html#f0-42884