MATLAB: Processing a HUGE number of timestamps

datenum

I have a cell array whose elements are time stamps in the format "Mon Apr 01 20:00:00 BST 2013". I have a very large number of these vectors. At the moment, I loop through each value in the vector and apply the below function. This loop taking up 99% of my processing time.
How can I remove the loop?
thanks
function myTimeOut = st_timestampConvert(myTime)
year = strtrim(myTime(end-4:end));
month = strtrim(myTime(5:8));
day = strtrim(myTime(9:10));
time = strtrim(myTime(11:19));
timezone = strtrim(myTime(20:23));
myTimeOut = convert_to_UTC(myTimeOut, timezone); %time zone conversion
myTimeOut = datenum([day '-' month '-' year ' ' time], 'dd-mmm-yyyy HH:MM:SS');
end

Best Answer

Without R2014b datetime, you can use regexprep to rearrange the bits of the string you want before calling datenum. It's many orders of magnitude faster than a loop, cellfun, or strsplit.
s2 = regexprep(s, '(\w+) (\w+) (\d+) ([0-9:]+) (\w+) (\d+)', '$3-$2-$6 $4');
tout = datenum(s2, 'dd-mmm-yyyy HH:MM:SS');
On my machine, to process 100k dates, the above two lines takes 2.1 seconds , most of it taken by the datenum operation. The regexp line is only 0.3 seconds.
There remains the problem of the time zone adjustment (which I believe should have come after the conversion to datenum in your example). Your convert_to_UTC is not part of matlab. Hopefully it can operate on cell arrays as well. Thus to extract the timezone:
tzones = regexp(s, '\w+(?= \d+$)', 'match', 'once');
tout = convert_to_UTC(tout, tzones); %Will this work?
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