max max - 11 months ago 55
Python Question

sum of products for multiple lists in python

Trying to imitate Excel's SUMPRODUCT function:

SUMPRODUCT(v1, v2, ..., vN) =
v1[0]*v2[0]*...*vN[0] + v1[1]*v2[1]*...*vN[1] + ... + v1[n]*v2[n]*...*vN[n]

where n is the number of elements in each vector.

This is similar to dot product, but for multiple vectors. I read the very detailed discussion of the regular dot product, but I don't know how to cleanly extend it to multiple vectors. For reference, I'm copying the optimized code proposed there, which I ported (trivially) to Python 3. BTW, for dot product, the last approach still wins in P3K.

def d0(v1,v2):
d0 is Nominal approach:
multiply/add in a loop
out = 0
for k in range(len(v1)):
out += v1[k] * v2[k]
return out

def d1(v1,v2):
d1 uses a map
return sum(map(mul,v1,v2))

def d3(v1,v2):
d3 uses a starmap (itertools) to apply the mul operator on an zipped (v1,v2)
return sum(starmap(mul,zip(v1,v2)))

Answer Source
import operator

def sumproduct(*lists):
    return sum(reduce(operator.mul, data) for data in zip(*lists))

for python 3

import operator
import functools

def sumproduct(*lists):
    return sum(functools.reduce(operator.mul, data) for data in zip(*lists))