MATLAB: Operations on large dataset

for loopunique

Hi, I want to apply functions on specific data stored in a table (Matrix). The data are of the form:
A = [100123 1 1 2500; 100123 1 2 2502; 100123 2 1 3000; 100123 2 2 3005; 100123 2 3 3003; 100456 1 1 5000; 100456 1 2 5005; 100456 1 3 5003; 100456 2 1 4300; 100456 2 2 4305]
For example I want to compute the mean of the values (4th column) that have the same values in the first and second column. That is the mean between 2500 and 2502 (key = 100123, serie = 1, data = 1 and 2), the mean between 3000, 3005, 3003 (key = 100123, serie = 2, data = 1, 2, 3) and so on.
Tnx for any suggestion, Gianluca

Best Answer

Use unique with the 'rows' option to extract the keys and their position and accumarray to get the mean according to the keys:
A = [100123 1 1 2500; 100123 1 2 2502; 100123 2 1 3000; 100123 2 2 3005; 100123 2 3 3003; 100456 1 1 5000; 100456 1 2 5005; 100456 1 3 5003; 100456 2 1 4300; 100456 2 2 4305];
[keys, ~, indices] = unique(A(:, [1 2]), 'rows');
keysmean = accumarray(indices, A(:, 4), [], @mean);
[keys keysmean]
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