NumPy：矩阵每n列求和

Question

我想对矩阵的每n列求和。我怎样才能在不使用for循环的情况下以一种简单的方式完成呢？这就是我现在所拥有的：

n = 3  #size of a block we need to sum over
total = 4  #total required sums
ncols = n*total
nrows = 10
x = np.array([np.arange(ncols)]*nrows)

result = np.empty((total,nrows))
for i in range(total):
    result[:,i] =  np.sum(x[:,n*i:n*(i+1)],axis=1)

结果是

^{pr2}$

如何将此操作矢量化？在

Answer 1

有一种方法：首先将x重塑为三维数组，然后在最后一个轴上求和：

>>> x.reshape(-1, 4, 3).sum(axis=2)
array([[ 3, 12, 21, 30],
       [ 3, 12, 21, 30],
       [ 3, 12, 21, 30],
       [ 3, 12, 21, 30],
       [ 3, 12, 21, 30],
       [ 3, 12, 21, 30],
       [ 3, 12, 21, 30],
       [ 3, 12, 21, 30],
       [ 3, 12, 21, 30],
       [ 3, 12, 21, 30]])