How do I calculate the mean of only positive values

I have a 3x24 array with negative and positive values, how do I calculate its mean value?

Answer 1

[Image Analyst]

Here's a well commented example:

m = 10 * rand(3, 24) - 5 % Create sample data (replace with your actual array).
posMap = m > 0 % Get map of where the positive values are.
m2 = m .* posMap; % Initializes m2.
m2(~posMap) = nan % Set negative values to nan so we can ignore them when we take the mean.
% Get mean of each column, meaning you average going down rows.
columnMeans = mean(m2, 1, 'omitnan')
% Get the mean of each row, meaning you average over all the columns in each row.
rowMeans = mean(m2, 2, 'omitnan')
% Get the mean of any positive value,  regardless of which row or column it lives in.
overallMean = mean(m2(:), 'omitnan')

Answer 2

[dpb]

mean(X(X>0))        % global mean

or

arrayfun(@(i) mean(X(X(:,i)>0,i)),1:size(X,2))  % column means

depending upon which mean(s) one is after.