max - 6 months ago 33

Python Question

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

```
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))
```