I have a matrix which contains 100 rows and 120 columns, I wonder how I can find the mean value for every 12 columns for each row. so I can have the annual mean. Thanks.
data=matrix(data,nrow = 100,ncol = 120)
For each row
tapply(r, gl(10, 12), mean) to it:
t(apply(data, 1, tapply, gl(10, 12), mean))
Note that the above does not use any properties of
mean so it generalizes to other aggregate functions by replacing
mean with some other function.
Another possibility which also generalizes is to reshape the matrix into a 3d array and take the mean over the indicated dimensions:
apply(array(data, c(100, 12, 10)), c(1, 3), mean)