Regexp: different behavior for the same type of expressions

Question

Giorgos Papakonstantinou 2013-9-19

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/87639-regexp-different-behavior-for-the-same-type-of-expressions

I want to capture everything except the tokens:

name, '_' and '.iv2'

name =
A7122
 >> filename'
 ans = 
    'A7122_60a.iv2'
    'A7122_60b.iv2'
    'A7122_70a.iv2'
    'A7122_70b.iv2'
    'A7122_90a.iv2'
    'A7122_90b.iv2'
    'A7122_100.iv2'
    'A7122_120.iv2'

I do this:

str=regexp(filename, [ '(?:[^' name '_])\w*(?:[^.iv2])' ], 'match');

And the answer is the following!

>> celldisp(str)
str{1}{1} =
60a
str{2}{1} =
60b
str{3}{1} =
0a
str{4}{1} =
0b
str{5}{1} =
90a
str{6}{1} =
90b
str{7}{1} =
00
str{8} =
       {}

I don't understand why regexp has a different behavior for i.e. in filename(1) and filename(3)

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Cedric 2013-9-19

编辑：Cedric 2013-9-20

Your mistake is that [^A7122_] doesn't stand for "any six letters expression that is not 'A7122 _'", but instead for "any character which is not in the pool of literals {'A', '7', '1', '2', '_' }". The same applies to [^.iv2]. This is why 70a and 70b for example are not matched, but you get instead 0a and 0b.

Giorgos Papakonstantinou 2013-9-20

Thank you very much Cedric! Very nice explanation!

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Answer 1

Vishal Rane 2013-9-19

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https://ww2.mathworks.cn/matlabcentral/answers/87639-regexp-different-behavior-for-the-same-type-of-expressions#answer_97199

编辑：Vishal Rane 2013-9-19

在 MATLAB Online 中打开

You can use:

regexprep( filename, [ name, '_|.iv2'], '')

Also

regexp( filename, [ name, '_(\w*).iv2'], 'tokens')

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Giorgos Papakonstantinou 2013-9-19

Thank you Vishal! Much more compact syntax! However, do you know why regexp has this behavior?

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Answer 2

Andrei Bobrov 2013-9-19

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链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/87639-regexp-different-behavior-for-the-same-type-of-expressions#answer_97201

编辑：Andrei Bobrov 2013-9-19

在 MATLAB Online 中打开

str = {'A7122_60a.iv2'
    'A7122_60b.iv2'
    'A7122_70a.iv2'
    'A7122_70b.iv2'
    'A7122_90a.iv2'
    'A7122_90b.iv2'
    'A7122_100.iv2'
    'A7122_120.iv2'}
cl = regexp(str,'(?<=_)\w*(?=\.)','match');
out = cat(1,cl{:});