This does the trick. apply(sapply(xyz_indices, function(xyz) edm[xyz[1], xyz[2], xyz[3], ]), 1, mean)
Jean On Fri, Dec 27, 2013 at 7:28 AM, Morway, Eric <[email protected]> wrote: > 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 > > [[alternative HTML version deleted]] > > ______________________________________________ > [email protected] mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide > http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. > [[alternative HTML version deleted]] ______________________________________________ [email protected] mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
