Extract numbers between two underscores.

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Mohammad
Mohammad el 20 de Jun. de 2014
Editada: Cedric el 21 de Jun. de 2014
Hi;
I am new to MATLAB and I need to extract numbers between two underscores. The only way I think this can be done is using the 'regexp' function. However, I am not sure about the expression that I need to the match it with. Can anyone help me?
Thanks;
Examples of my strings are:
Color_84_2014-01-31-16-49-31-702.jpg
Color_85_2014-01-31-16-49-31-732.jpg
Color_86_2014-01-31-16-49-31-762.jpg
Color_87_2014-01-31-16-49-31-792.jpg
So I just need the number 84,85,86,87,...
Thanks Again!
  1 comentario
Cedric
Cedric el 21 de Jun. de 2014
Do you have all these strings in e.g. a file and you want to extract all the numbers in one shot, or are you processing these string one at a time?

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Respuestas (3)

dpb
dpb el 20 de Jun. de 2014
>> s='Color_84_2014-01-31-16-49-31-702.jpg';
>> sscanf(s,'Color_%d_%d-%d-%d-%d-%d-%d-%d.jpg')
ans =
84
2014
1
31
16
49
31
702
>>

Geoff Hayes
Geoff Hayes el 20 de Jun. de 2014
You could just use the strfind function to find the underscores, and then extract the data in between those two values:
str = 'Color_84_2014-01-31-16-49-31-702.jpg';
idcs = strfind(str,'_');
num = str2num(str(idcs(1)+1:idcs(2)-1));
A regexp alternative probably exists. Try the above and see what happens!
  3 comentarios
Geoff Hayes
Geoff Hayes el 21 de Jun. de 2014
Neat - I wondered about that!
Cedric
Cedric el 21 de Jun. de 2014
Editada: Cedric el 21 de Jun. de 2014
The pattern in the first approach matches:
  • One or more numeric characters: '\d+', where \d is the wildcard/operator for numeric characters and + is the quantifier "one or more".
  • Preceded by an underscore: '(?<=_)' where (?<=..) is a positive "lookbehind" for ...
  • Followed by an underscore: '(?=_)' where (?=..) is a positive "lookahead" for ...
Note that the "lookaround" operators are not included in the output.
The second approach is based on tokens extraction. The pattern says: an underscore followed by one or more numeric characters followed by an underscore, which is the following match '_\d+_', but we group the \d+ in a token (defined by the framing parentheses) and we ask REGEXP to extract just the token (with the 3rd 'tokens' argument in the call).

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Jos (10584)
Jos (10584) el 20 de Jun. de 2014
str = 'Color_84_2014-01-31-16-49-31-702.jpg'
num = sscanf(str,'Color_%d')
If your strings are stored in a cell array of strings C, use cell fun
num = cellfun(@(str) sscanf(str,'Color_%d') , C)
  1 comentario
dpb
dpb el 20 de Jun. de 2014
>> sscanf(s,'Color_%d')
ans =
84
Gotta have enough formats to convert. Also note that despite the title there are dashes as well as underscores in the string.

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