MATLAB: How to extract multiple numbers with regexp

MATLABregexp

I am trying to pull the ID from the following string.

'blah String XX blah'

where XX is the number that could be anything from 0 – 9999. I have tried the regular expression below but this only works for 0 – 9. Any ideas?

[aa,bb] = regexp(sss,'String (\d+)')

Best Answer

id = regexp(sss, '(?<=String\s+)(\d+)', 'match', 'once');

The result will be a cell array of string containing the matched string

If you want it more directly then

id = regexprep(sss, '(.*?String\s+)(\d+)(.*)', '$2', 'once');

The result would be a string directly.

The first version, the regexp version, is looking for digits proceeded by 'String' with the 'String' part marked up to indicate it is not to form part of the match.

The second version, the regexprep version, is matching on beginning of line to the first occurrence of 'String' as one group, matching on the digits as a second group, and matching to the end of the line as a third group, and is replacing the three matches with the content of the second group, thus effectively throwing away everything before and after the digits.

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MATLAB: Regex: How to match an empty string

Use

regexp(a,'^$','emptymatch')

MATLAB: How to open files whose name matches a string from another file name

Assuming timestamps are all of the same form, you can find them with regexp:

%filesgroup1: a cell array of string representing file names from group 1
tstamps1 = regexp(filesgroup1, '\d{4}-\d{2}-\d{2}T\d{2}-\d{2}-\d{2}', 'match', 'once');

You can do the exact same thing for group 2:

filesgroup2: a cell array of string representing file names from group 2
tstamps2 = regexp(filesgroup1, '\d{4}-\d{2}-\d{2}T\d{2}-\d{2}-\d{2}', 'match', 'once');

You can then check which timestamps from group 2 are in group 1 with ismember:

isingroup1 = ismember(tstamps2, tstamps1);

Finally, you use the logical array returned by ismember to filter your group2 filenames:

files2match1 = filesgroup2(isingroup1);

Note: the regexp matches 4 digits, followed by '-', followed by 2 digits, followed by '-', followed by 2 digits, followed by 'T', followed by 2 digits, followed by '-', followed by 2 digits, followed by '-', followed by 2 digits.

Best Answer

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MATLAB: Regex: How to match an empty string

MATLAB: How to open files whose name matches a string from another file name

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