Question

Suppose I have a data array,

dat <- array(NA, c(115,45,248))

Q1: What I do if I want to get a new data array,

datnew <- array(NA, c(115,45,248))

in which, all the positive value remain and the negative value changed to NA?

Q2: What I do if I want to get a new data array,

 datnew <- array(NA,c(115,45,31))

by averaging with the third dimension, but only averaging every 8 values?

Thanks a lot.

Answer 1

For question 2,

you can reverse the order of the dimensions, then add a dimension representing the groups to average over, then use apply:

tmp <- array( 1:32, c(2,2,8) )
tmp2 <- array( aperm(tmp), c(4,2,2,2) )
apply( tmp2, 2:4, mean )