行交换在np数组python中

Question

我想在python中的np.array中执行换行。我想要的是取数组的第一行并将其放在数组的末尾。我有代码可以交换两行，如下所示：

data_ask_bid = data_ask_bid[((0 <= data_ask_bid.index.weekday <= 3) | (data_ask_bid.index.weekday == 4 & data_ask_bid.index.hour < 22))]

但是这段代码执行第一行和最后一行之间的交换。我想把第一行放在最后。我怎么能这样做？

初始矩阵如下：

import numpy as np
my_array = np.arrange(25).reshape(5, 5)
print my_array, '\n'

def swap_rows(arr, frm, to):
   arr[[frm, to],:] = arr[[to, frm],:]

//swap_rows(my_array, 0, 8)
//print my_array
my_array[-1] = my_array[0]
print my_array

预期结果如下：

[[ 0  1  2  3  4]
[ 5  6  7  8  9]
[10 11 12 13 14]
[15 16 17 18 19]
[20 21 22 23 24]] 

编辑：我正在尝试在我的矩阵中执行相同的操作，如下所示：

但它不会改变任何事情。我的代码如下：

[[ 5  6  7  8  9]
[10 11 12 13 14]
[15 16 17 18 19]
[20 21 22 23 24]
[ 0  1  2  3  4]] 

我得到了相同的数组。

Answer 1

您可以使用np.roll -

np.roll(my_array,-1,axis=0)

示例运行 -

In [53]: my_array
Out[53]: 
array([[ 0,  1,  2,  3,  4,  5,  6,  7,  8],
       [ 9, 10, 11, 12, 13, 14, 15, 16, 17],
       [18, 19, 20, 21, 22, 23, 24, 25, 26],
       [27, 28, 29, 30, 31, 32, 33, 34, 35],
       [36, 37, 38, 39, 40, 41, 42, 43, 44],
       [45, 46, 47, 48, 49, 50, 51, 52, 53],
       [54, 55, 56, 57, 58, 59, 60, 61, 62],
       [63, 64, 65, 66, 67, 68, 69, 70, 71],
       [72, 73, 74, 75, 76, 77, 78, 79, 80]])

In [54]: np.roll(my_array,-1,axis=0)
Out[54]: 
array([[ 9, 10, 11, 12, 13, 14, 15, 16, 17],
       [18, 19, 20, 21, 22, 23, 24, 25, 26],
       [27, 28, 29, 30, 31, 32, 33, 34, 35],
       [36, 37, 38, 39, 40, 41, 42, 43, 44],
       [45, 46, 47, 48, 49, 50, 51, 52, 53],
       [54, 55, 56, 57, 58, 59, 60, 61, 62],
       [63, 64, 65, 66, 67, 68, 69, 70, 71],
       [72, 73, 74, 75, 76, 77, 78, 79, 80],
       [ 0,  1,  2,  3,  4,  5,  6,  7,  8]])