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How to filter data?

Asked by Thor

Thor (view profile)

on 16 Jan 2013

Dear all,

I want to filter a matrix by its date vector. The datevector has the format: HH:MM:SS. I want to sum up all the data with the same month and year. How can I do that?



Thor (view profile)


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1 Answer

Answer by Jan Simon

Jan Simon (view profile)

on 16 Jan 2013
Accepted answer
dateAsString = {'31.02.2013 11:22:33'; '31.05.2013 11:22:33'}
dateAsVector = datevec(datestr, ' HH:MM:SS');
yearAndMonth = 100 * dateAsVector(:, 1) + dateAsVector(:, 2);

Now you get values like [201302, 201305] and summing can be done by accumarray directly.


Walter Roberson

Walter Roberson (view profile)

on 16 Jan 2013

You would probably not want to use those values as direct subscripts into accumarray: you would probably want to unique() them and use the indices. Otherwise your array is going to end up being up to 240000 long with not many entries used.

Jan Simon

Jan Simon (view profile)

on 16 Jan 2013

You are right, Walter, and even for a FOR loop approach using the indices obtained by UNIQUE is better.

Jan Simon

Jan Simon (view profile)

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