3D binning in Matlab

Question

I wonder if there is a faster solution to the problem below than using loops.

I have a set of points scattered in 3D space, with a value assigned to each point. So something like dataPoints = [x1, y1, z1, v1; x2, y2, z2, v2; ...] dataPoints = [x1, y1, z1, v1; x2, y2, z2, v2; ...] dataPoints = [x1, y1, z1, v1; x2, y2, z2, v2; ...] . The 3D space is evenly split into subvolumes dx × dy × dz . I need to create a matrix containing the sum of v 's in each subvolume.

The number of subvolumes and data points can be pretty big, on the order of 1 million each. So loops are really to be avoided.

I can easily find out, which subvolume a point belongs to:

ix(:) = floor(x(:) / dx) + 1;
iy(:) = floor(y(:) / dy) + 1;
iy(:) = floor(z(:) / dz) + 1;

However now I need to add up all points with the same tuple (ix, iy, iz) . Any ideas?

Answer 1

使用accumarray

 sums = accumarray( { iy(:), ix(:), iz(:) }, v(:) );