Multi tool use

Calculating mean over column with condition

So my question is as follows: I have a matrix (let's take

A = [ 1 11 22 33; 44 13 12 33; 1 14 33 44,]

A = [ 1 11 22 33; 44 13 12 33; 1 14 33 44,]

as an example) where I want to calculate the mean for all columns separately. The tricky part is that I only want to calculate the mean for those numbers in each column which are greater than the column 25th percentile.

I was thinking to simply create the 25th percentile and then use this as a criterion for selecting rows. This, unfortunately, does not work.

In order to further clarify: What should happen is to go through each column and calculate the 25th percentile

prctile(A,25,1)

prctile(A,25,1)

And then calculating the mean only for those numbers which are respectively to their column bigger than the percentile.

Any help?
Thanks!

1 Answer
1

You can create a version of A which is NaN for values below the 25th percentile, then use the 'omitnan' flag in mean to exclude those points:

A

NaN

'omitnan'

mean

A = [1 11 22 33; 44 13 12 33; 1 14 33 44];
B = A; % copy to leave A unaltered
B( B <= prctile(B,25,1) ) = NaN; % Turn values to NaN which we want to exclude
C = mean( B, 1, 'omitnan' ); % Omit the NaN values from the caculation
% C >>
% [ 15.33 13.50 27.50 36.67 ]


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