MATLAB Answers


How to filter data?

Asked by Thor
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?



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1 Answer

Jan Simon
Answer by Jan Simon
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.


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
on 16 Jan 2013

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

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