In the larger problem I'm attempting to solve, I read a 2Gb file
into a 4D array, where the first 3 dimensions are related to space
(x, y, z), and the 4th dimension is time. My goal is to find the
average of specific x, y, z-indices for each time step.
A small, reproducible example starts like this:
edm <- array(rnorm(20*20*4*50), dim=c(20,20,4,50))
xyz_indices <- list(c(2,10,1), c(4,5,1), c(6,7,1), c(19,13,1))
What's the best way to calculate the average of the x, y, z
indices specified in the "xyz_indices" list for each of the 50 time
steps represented by the 4th dimension of "edm"? In other words,
I want to end up with a time series of length 50 where each value of
the series is the average of the 4 xyz_indices.
Eric
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