I have a matrix like this:
mt1=matrix(1:144,ncol=12,nrow=12)
And I would like only to calcutate the mean only for 3 values in a row. These are the three first values:
[,1] [,2] [,3]
[1,] 1 13 25
the mean should be 13.
And the same for the next three values and the same for the next three values.. And so on and on until the end of rows.
I know I have to use the apply function, but I cannot figure out to apply the mean only to specific values that is only to a sequence of rows, and then on the next sequence of rows, and get then as a result a vector with the means of only 3 values per row.
Thanks a lot!
Try:
> apply(mm, 1, function(x) mean(x[1:3]))
[1] 13 14 15 16 17 18 19 20 21 22 23 24
Mean of 1,13,25 is not 29 but 13
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