Extracting numbers from mixed string
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I have filenames saved as strings such as '2001_06m'. Sometimes the files are inconsistently named as '2001_6m' (missing the zero before the 6) or '2001_06' (missing the m at the end). What code would I use to extract the non-zero integers after underscore in all cases (i.e. output = 6)?
And separately, what code would I use to extract the numbers before the underscore (usually they are 4 digits long, but sometimes 3 digits, i.e. '001' instead of '2001')?
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Accepted Answer
Jan
on 7 Oct 2018
Edited: Jan
on 8 Oct 2018
s = '2001_06m';
d = sscanf(s, '%d_%d')
ans =
2001
6
Easier and faster than regexp.
[EDITED] If the input is a cell string:
C = {'2001_06m', '002_77q'};
S = sprintf('%s ', C{:});
S(S < '0' | S > '9') = ' '; % Mask all non-numbers
Num = sscanf(S, '%d %d ', [2, Inf]);
2 Comments
Guillaume
on 8 Oct 2018
To be honest, none of the solutions are vectorised. Vectorising strsplit wouldn't be easy either. It wouldn't be too hard to vectorise the regexp solution, but sscanf is certainly more elegant.
More Answers (3)
Guillaume
on 7 Oct 2018
Edited: Guillaume
on 8 Oct 2018
A possible regexp version would be:
str2double(regexp(filename, '(\d+)_(\d+)', 'tokens', 'once'))
edit: following the discussion in Jan's answer, a vectorised version for when filenames is a cell array of char arrays or a string array:
tokens = regexp(filenames, '(\d+)_(\d+)', 'tokens', 'once');
str2double(vertcat(tokens{:}))
Note that the vertcat call will fail if a filename does not match the pattern.
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Stephen23
on 8 Oct 2018
Edited: Stephen23
on 8 Oct 2018
Fully vectorized, one line, and more efficient than regexp and/or str2double:
>> C = {'2001_06m','2001_7m','2001_08'};
>> sscanf(sprintf('%sm',C{:}),'%*d_%d%*[m]') % second number
ans =
6
7
8
>> sscanf(sprintf('%sm',C{:}),'%d_%*d%*[m]') % first number
ans =
2001
2001
2001
>> sscanf(sprintf('%sm',C{:}),'%d_%d%*[m]') % both numbers
ans =
2001
6
2001
7
2001
8
"...usually they are 4 digits long, but sometimes 3 digits, i.e. '001' instead of '2001'"
My answer works regardless of the number of digits in the numbers.
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dpb
on 7 Oct 2018
v=str2double(strip(splitstr(s,'_'),'m')); % chuckles...
In reality, write a regexp expression is the more general solution but I have to spend too much time figuring out the syntax and am too impatient... :)
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