MATLAB: Deleting/selecting and subsetting specific slices in a multi-dimensional array

Question

Hello,

I have three variables that are three-dimensional arrays of the size 699 (say, x or rows) x 699 (say, y or columns) x 60 (say, z or slices). I have first computed certain indices using certain conditions. E.g.,

idxs = Z > 5000 & W > 1 & M_tot > 0.05; % Idx is now a logical array of size 699 x 699 x 60.

Now, for further analysis, I am interested in keeping only those slices that satisfy the above conditions. In other words, I want to delete those slices where the idxs at a given x,y are zeros for all z. I used the any function below to create a subset:

subset_idx = any(idxs,3);

This creates a 699 x 699 logical array where I would like to keep all the points corresponding to 1 and delete all the rows and columns corresponding to a 0. This should give me a subset array of size nx, ny, 60 where nx and ny are much less than 699. How do I achieve this?

I tried something like this:

todelete_idx = ~(any(idxs,3)); Size : 699 x 699 logical

idxs(todelete_idx,:) = [];

However, this produces an error since the todelete_idx is a two-dimensional array and I am unable to subset it like this. What is the way around this?

Answer 1

This may not be the most efficient way, but you can take that 2D logical array and rebuild your 3D logical array:

subset_3D = and(subset_idx,true(1,1,size(idxs,3)));