Hi All, I have this example program: import numpy as np import numpy.random as rnd def dim_weight(X): weights = X[0] volumes = X[1]*X[2]*X[3] res = np.empty(len(volumes), dtype=np.double) for i,v in enumerate(volumes): if v>5184: res[i] = v/194.0 else: res[i] = weights[i] return res # TEST N = 10 X = rnd.randint( 1,25, (4,N)) print dim_weight(X) I want to implement the dim_weight() function effectively. But I'm not sure how to construct a numpy expression that does the same think for me. I got to this point: def dim_weight(X): weights = X[0] volumes = X[1]*X[2]*X[3] dweights = volumes/194.0 return ( weights[weights>5184] , dweights[weights<=5184] ) # ??? I don't know how to preserve the order of the elements and return the result in one array. Maybe I need to do create a matrix multiply matrix? But don't know how. Thanks, Laszlo -- This message has been scanned for viruses and dangerous content by MailScanner, and is believed to be clean.