Question

我如何从汇总表中提取第一栏,或从第5栏到第5栏+n栏中提取一栏?

The scenario is that I have a matrix, of dim=(i,j), then I want to look a contiguous blocks of column of length n. So I want to look at the matrix from column0 to column n, then at column1 to column n+1. etc. Until I reach the end of my matrix.

增编

>>> mat=array(range(0,20)).reshape(2,10)
>>> mat
array([[ 0,  1,  2,  3,  4,  5,  6,  7,  8,  9],
       [10, 11, 12, 13, 14, 15, 16, 17, 18, 19]])

Given n=8. I want to extract the first 8 columns.

然后,汇总表从[1,11]栏改为[8,18]栏

然后,汇总表从[2,12]栏改为[9,19]栏

Answer 1

>>> mat[:, 0:8]
array([[ 0,  1,  2,  3,  4,  5,  6,  7],
       [10, 11, 12, 13, 14, 15, 16, 17]])
>>> mat[:, 1:9]
array([[ 1,  2,  3,  4,  5,  6,  7,  8],
       [11, 12, 13, 14, 15, 16, 17, 18]])

Answer 2

在Sven Marnach的答复的基础上,如果你想在<代码>mat[:0:8]上进行计算,然后在<代码>mat[:1:9]上进行计算,则你可以“一次”进行3维矩阵的所有计算。

In [119]: x = np.lib.stride_tricks.as_strided(mat, shape = (3,2,8), strides = mat.itemsize*np.array([1,mat.shape[-1],1]))

In [120]: x
Out[120]: 
array([[[ 0,  1,  2,  3,  4,  5,  6,  7],
        [10, 11, 12, 13, 14, 15, 16, 17]],

       [[ 1,  2,  3,  4,  5,  6,  7,  8],
        [11, 12, 13, 14, 15, 16, 17, 18]],

       [[ 2,  3,  4,  5,  6,  7,  8,  9],
        [12, 13, 14, 15, 16, 17, 18, 19]]])

例如,为了找到各行各业的内产产品,你可以把这三人同起来。

In [127]: np.sum(x[:,0,:]*x[:,1,:],axis = -1)
Out[127]: array([420, 564, 724])

a. 不使用甲型 lo:

In [128]: for i in range(3):
   .....:     print(np.sum(mat[0,i:i+8]*mat[1,i:i+8]))
   .....:     
   .....:     
420
564
724

友情链接