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)

[Cedric]

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]

Thank you very much Cedric! Very nice explanation!

Answer 1

[Vishal Rane]

You can use:

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

Also

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

[Giorgos Papakonstantinou]

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

Answer 2

[Andrei Bobrov]

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{:});

[Giorgos Papakonstantinou]

Thank you Andrei! Do you know why is this happening?

[Andrei Bobrov]

Please read about regexp, parts:

- Regular expression :

about

Metacharacters ( \w ),

Quantifiers ( expr* ),

Lookaround Assertions ( expr(?=test) and (?<=test)expr )