Accessing the data in MATRIX based on condition

I have a 9000 by one Matrix.As an Example considering the following

X Y Z P

5 5 5 900

5 5 10 800

5 5 15 1200

5 10 5 300

5 10 10 560

5 10 15 900

I want compute average P at each Y, that means all values of P when Y is 5.Similary when y is 10....It is just a example.Next x goes to 10 and same varies

Answer 1

[Walter Roberson]

findgroups() and then splitapply()

https://www.mathworks.com/help/matlab/ref/findgroups.html#bux3dup

https://www.mathworks.com/help/matlab/ref/splitapply.html

However, if your array is as regular as it looks, you should probably just reshape and mean() along the appropriate plane (you might need a permute() in there, and maybe two rounds of reshape())