Hi, I have a set of n points with real coordinates between 0 and 1, given by two numpy arrays x and y, with a value at each point represented by a third array z. I am trying to then rasterize the points onto a grid of size npix*npix. So I can start by converting x and y to integer pixel coordinates ix and iy. But my question is, is there an efficient way to add z[i] to the pixel given by (xi[i],yi[i])? Below is what I am doing at the moment, but the for loop becomes very inefficient for large n. I would imagine that there is a way to do this without using a loop? --- import numpy as np n = 10000000 x = np.random.random(n) y = np.random.random(n) z = np.random.random(n) npix = 100 ix = np.array(x*float(npix),int) iy = np.array(y*float(npix),int) image = np.zeros((npix,npix)) for i in range(len(ix)): image[ix[i],iy[i]] = image[ix[i],iy[i]] + z[i] --- Thanks for any advice, Thomas