# Mean of array columns with condition

6 views (last 30 days)
Mariella Dreißig on 18 Nov 2019
Answered: Philippe Lebel on 18 Nov 2019
I have an array of which I need the mean of each column (X). Additionally, I have a logical array of which rows meet a condition and should be included in the mean (Y).
Naturally, the mean function in MATLAB calculates each column mean, but when I insert the logical vector for the row selection, the mean is calculated for the whole array. How do I fix this for computing the mean of each column in X for the valid indices of Y?
When entering
means_active = mean(X(Y), :);
I get the error 'Reference to a cleared variable mean.', though I don't want to use any variable 'mean' but the built-in function 'mean'.
Mariella Dreißig on 18 Nov 2019
I found a workaround though, thanks :)

Philippe Lebel on 18 Nov 2019
I tested my solution with these matrices:
a = rand(6,3)
B=[1;0;1;1;0;1];
means_active = mean(a(logical(B)),2);
seems to work for me. (i was forced to cast B as logical because i manually declared the values inside the list as integers)

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