在python中使用argsort进行排序
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Sort using argsort in python
提问by user2958912
I try to sort an array:
我尝试对数组进行排序：
import numpy as np
arr = [5,3,7,2,6,34,46,344,545,32,5,22]
print "unsorted"
print arr
np.argsort(arr)
print "sorted"
print arr
But the output is:
但输出是：
unsorted
[5, 3, 7, 2, 6, 34, 46, 344, 545, 32, 5, 22]
sorted
[5, 3, 7, 2, 6, 34, 46, 344, 545, 32, 5, 22]
The array does not change at all
数组根本不改变
采纳答案by askewchan
There are two issues here; one is that np.argsortreturns an array of the indiceswhich would sort the original array, the second is that it doesn't modify the original array, just gives you another. This interactive session should help explain:
这里有两个问题；一个是np.argsort返回一个索引数组，它可以对原始数组进行排序，第二个是它不会修改原始数组，只是给你另一个。这个交互式会话应该有助于解释：
In [59]: arr = [5,3,7,2,6,34,46,344,545,32,5,22]
In [60]: np.argsort(arr)
Out[60]: array([ 3, 1, 0, 10, 4, 2, 11, 9, 5, 6, 7, 8])
Above, the [3, 1, 0, ...]means that item 3in your original list should come first (the 2), then item 2should come (the 3), then the first (index is 0, item is 5) and so on. Note that arris still unaffected:
上面的[3, 1, 0, ...]意思是3原始列表中的 item应该先出现 (the 2)，然后 item2应该出现 (the 3)，然后是第一个 (index is 0，item is 5)，依此类推。请注意，arr仍然不受影响：
In [61]: arr
Out[61]: [5, 3, 7, 2, 6, 34, 46, 344, 545, 32, 5, 22]
You might not need this array of indices, and would find it easier to just use np.sort:
您可能不需要这个索引数组，并且会发现使用它更容易np.sort：
In [62]: np.sort(arr)
Out[62]: array([ 2, 3, 5, 5, 6, 7, 22, 32, 34, 46, 344, 545])
But this still leaves arralone:
但这仍然是arr单独的：
In [68]: arr
Out[68]: [5, 3, 7, 2, 6, 34, 46, 344, 545, 32, 5, 22]
If you want to do it in place (modify the original), use:
如果你想就地做（修改原来的），使用：
In [69]: arr.sort()
In [70]: arr
Out[70]: [2, 3, 5, 5, 6, 7, 22, 32, 34, 46, 344, 545]
回答by TerryA
np.argsortdoesn't sort the list in place, it returns a list full of indicies that you are able to use to sort the list.
np.argsort不会就地对列表进行排序，它会返回一个完整的索引列表，您可以使用这些索引对列表进行排序。
You must assign this returned list to a value:
您必须将此返回的列表分配给一个值：
new_arr = np.argsort(arr)
Then, to sort the list with such indices, you can do:
然后，要使用此类索引对列表进行排序，您可以执行以下操作：
np.array(arr)[new_arr]
回答by Phil Cooper
回答by JoshAdel
If you want your array sorted in-place you want arr.sort():
如果你想你的数组就地排序，你想要arr.sort()：
In [1]: import numpy as np
In [2]: arr = [5,3,7,2,6,34,46,344,545,32,5,22]
In [4]: print arr
[5, 3, 7, 2, 6, 34, 46, 344, 545, 32, 5, 22]
In [5]: arr.sort()
In [7]: print arr
[2, 3, 5, 5, 6, 7, 22, 32, 34, 46, 344, 545]
