列表列表与列表列表相乘

Question

V = [[10,20],[40,50]]
I = [[1,2],[4,5]]
print(V*I)

** output is:TypeError: can't multiply sequence by non-int of type 'list'

**I want the output something like V*I = [[10,40],[160,250]]

Answer 1

TL;DR

[[x * y for x, y in zip(i, v)] for i, v in zip(I, V)] most general and most pythonic.

Pure Python

• Specifically for nested lists of 2 elements:

  [[x1 * x2, y1 * y2] for (x1, y1), (x2, y2) in zip(V, I)]

• More generally, for nested lists of any length:

  [[x * y for x, y in zip(i, v)] for i, v in zip(I, V)]

Numpy

• Nested lists where all the inner lists have the same number of elements:

  (np.array(I) * np.array(V)).tolist()

• Nested lists when inner lists might have different number of elements but corresponding lists have same number of elements:

  [(np.array(i) * np.array(v)).tolist() for i, v in zip(I, V)]

The last one is pretty ugly but numpy is not designed to handle matrix with different number of columns.

Answer 2

Using zip and list comprehension.

Ex:

V = [[10,20],[40,50]]
I = [[1,2],[4,5]]
res = []
for i in zip(V, I):
    res.append([j * k for j, k in zip(*i)])
print(res)

Output:

[[10, 40], [160, 250]]

Answer 3

当然不是最佳工具，但是在普通的Python中，这种嵌套的理解将适用于2D矩阵：

[[a*b for a, b in zip(v, i)] for v, i in zip(V, I)]

Answer 4

>>> [[x*y for x,y in zip(*t)] for t in zip(V, I)]
[[10, 40], [160, 250]]

Answer 5

Use numpy :

import numpy as np

V = np.matrix([[10,20],[40,50]])
I = np.matrix([[1,2],[4,5]])

np.multiply(V,I)

Gives:

[[ 10  40]
 [160 250]]