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How do I get the date out of a filename using regexp?

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Shayma Al Ali
Shayma Al Ali on 21 Nov 2019
Answered: Stephen on 21 Nov 2019
Currently, I have a list of files that are saved as the following 'xxx_2014_06_03_00_00_01'. I'd like to extract the date in the file name using regexp. Currently, my code is:
dt=datetime(fdate,'InputFormat','dd-MM-yyyy HH:mm:ss')
However, whenever I test it out, fdate is always returned as empty. I'm extremely confused about regexp and how to use it.

Accepted Answer

Star Strider
Star Strider on 21 Nov 2019
There are likely several ways to approach this. I would do it a bit differently:
str = 'xxx_2014_06_03_00_00_01';
fdate = regexp(str, '\d*','match');
datev = str2double(fdate);
producing (here):
dt =
03-Jun-2014 00:00:01
I left these as separate lines to demonstrate how it works. The str2double call could be inserted into the datetime call.

More Answers (2)

Jeremy on 21 Nov 2019
Edited: Jeremy on 21 Nov 2019
str = 'xxx_2014_06_03_00_00_01';
id = regexp(str,'\d')
id =
5 6 7 8 10 11 13 14 16 17 19 20 22 23
These are the indices of str that contain numeric digits. If you know that the 'xxx' part of the filename will not contain numeric digits, then you could then go ahead and say
year = str2double(str(id(1:4)));
month = str2double(str(id(5:6)));
Alternatively, you could use 'strtok' and pass it the underscore character as a delimiter to get a string of the datetime and convert those to integers. This is likely less efficient, though.

Stephen on 21 Nov 2019
In one line without intermediate indices or double vector:
>> str = 'xxx_2014_06_03_00_00_01';
>> dtm = datetime(regexp(str,'(\d+_?){6}','match','once'),'InputFormat','yyyy_MM_dd_HH_mm_ss')
dtm =
03-Jun-2014 00:00:01


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