Help with extracting part of a string
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I have the string "2DVIS_data_08_40fs", and I want to extract the numbers included between the last underscore '_' and the last two letters 'fs', in this case 40. Given the string "2DVIS_data_08_120fs", I want as output 120 and so on. How can I do this? thanks
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Accepted Answer
Chad Greene
on 26 Sep 2014
Guillame's answer is best, and it's probably good to learn how to use the power of regexp. But if you want a more intuitive-for-beginners approach, find the indices of the underscores, find the indices of fs, and then return everything between them:
somestring = '2DVIS_data_08_40fs';
underscore_indices = strfind(somestring,'_');
fs_indices = strfind(somestring,'fs');
yourNumber = str2double(somestring(underscore_indices(end)+1:fs_indices(end)-1))
More Answers (3)
Stephen23
on 26 Sep 2014
Edited: Stephen23
on 27 Sep 2014
Given a literal interpretation of your statement "extract the numbers included between the last underscore '_' and the last two letters 'fs'", this could be done using the following regexp match string:
>>A = {'2DVIS_data_08_120fs','2DVIS_data_08_40fs'};
>>B = regexp(A,'(?<=_)\d+(?=fs$)','once','match')
B =
'120' '40'
This match string locates one or more digits located between an '_' and the last two characters of the string (which must be 'fs'). If the strings are always of the same format, then matching of the last two characters would be enough.
Guillaume
on 26 Sep 2014
Use regexp, you haven't explained the pattern in great details, the following may be what you want:
elems = regexp(s, '_(\d+)_[^_]*(..)$', 'tokens', 'once');
number = str2double(elems{1});
string = elems{2};
It will match any pattern with _, followed by 1 or more digit (an integer), followed by _, followed by any 0 or more characters not including _, followed by two characters at the end of the string. It extracts the integer and the last two characters.
2 Comments
Guillaume
on 27 Sep 2014
Realised I misunderstood the pattern. Stephen's or the following would work:
number = str2double(regexp(s, '_(\d+)..$', 'tokens', 'once'));
If you want to ensure that the last two characters are letters:
number = str2double(regexp(s, '_(\d+)[a-zA-Z]{2}', 'tokens', 'once'));
Or if it's always 'fs':
number = str2double(regexp(s, '_(\d+)fs', 'tokens', 'once'));
Albert Passy
on 14 Nov 2018
"Some people, when confronted with a problem, think "I know, I'll use regular expressions." Now they have two problems."
Regexes are expressive, compact and cryptic. reserve them for complex problems.
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