Question

我有以下表格的数据：

#---------------------
# Data
#---------------------
p   q   r
2   8   14
2   9   22
1   5   19
2   7   19
3   11  13
2   7   20
1   4   15
3   12  17
1   4   14
1   5   20
2   7   17
3   10  13
3   11  20
3   11  14
1   6   18
3   12  16
2   9   21
3   10  19
2   8   13
1   6   22
1   4   13
2   8   15
3   12  15
3   10  16
2   9   16
1   5   16
1   6   21

现在我需要使用NumPy以下列方式对这些数据进行排序：

列p。
第q列的升序。
列r。降序。

我使用了以下代码，但它没有正确排序：

import numpy as np

data = open('data.dat', "r")
line = data.readline()
while line.startswith('#'):
    line = data.readline()
data_header = line.split("\t")
data_header[-1] = data_header[-1].strip()

_data_ = np.genfromtxt(data, comments='#', delimiter='\t', names = data_header, dtype = None, unpack = True).transpose()            # Read space-separated values in engine data file.
sorted_index =  np.lexsort((_data_['r'][::-1], _data_['q'], _data_['p']))
_data_ =  _data_[sorted_index]
print (_data_)

Ouptut

这种排序方法可能有什么问题？

Answer 1

问题是，当您撤销r列时，numpy并不知道您的指数会发生变化。解决方法分两步进行，但它不会优雅：

pre_sort_index = np.lexsort((_data_['r'],), axis=0)[::-1]
sorted_index =  np.lexsort((_data_[pre_sort_index]['q'], _data_[pre_sort_index]['p']))
_data_ =  _data_[pre_sort_index][sorted_index]

Answer 2

实际上，您快到了！只需在代码中修改这一行（减号而不是[::-1]）就可以了

sorted_index =  np.lexsort((-_data_['r'], _data_['q'], _data_['p']))

更一般地讲，这个减号有点可笑，但只要您只处理数字值，它就应该起作用

# 2D array will be sorted first by p, then by q (if p is the same), then by r
sortkeys = ['p','q','r']
# 1 is ascending/forward sort, -1 is descending/reverse sort
sortdirection = [1,1,-1]
# need [::-1] as its sorts with last element first...
ind = np.lexsort(tuple([(_data_[skey])*sdir for skey,sdir in
                                     zip(sortkeys[::-1],sortdirection[::-1])]))
_data_ = _data_[ind]
for i in _data_:
    print(i)

输出：

(1, 4, 15)
(1, 4, 14)
(1, 4, 13)
(1, 5, 20)
(1, 5, 19)
(1, 5, 16)
(1, 6, 22)
(1, 6, 21)
(1, 6, 18)
(2, 7, 20)
(2, 7, 19)
(2, 7, 17)
(2, 8, 15)
(2, 8, 14)
(2, 8, 13)
(2, 9, 22)
(2, 9, 21)
(2, 9, 16)
(3, 10, 19)
(3, 10, 16)
(3, 10, 13)
(3, 11, 20)
(3, 11, 14)
(3, 11, 13)
(3, 12, 17)
(3, 12, 16)
(3, 12, 15)

如何在Python中反转和转发NumPy 2D数组？

2 个答案: