argsort()函式

<span style="font-size:18px;">>>> x = np.array([3, 1, 2])
>>> np.argsort(x) #按升序排列
array([1, 2, 0])
>>> np.argsort(-x) #按降序排列
array([0, 2, 1])

>>> x[np.argsort(x)] #通過索引值排序後的陣列
array([1, 2, 3])
>>> x[np.argsort(-x)]
array([3, 2, 1])

另一種方式實現按降序排序：

>>> a = x[np.argsort(x)]
>>> a
array([1, 2, 3])
>>> a[::-1]
array([3, 2, 1])   </span>
 

sort函式是list列表中的函式，而sorted可以對list或者iterator進行排序

1、用sort函式對列表排序時會影響列表本身，而sorted不會

>>> a = [1,2,1,4,3,5]
	>>> a.sort()
	>>> a
	[1, 1, 2, 3, 4, 5]

>>> a = [1,2,1,4,3,5]
	>>> sorted(a)
	[1, 1, 2, 3, 4, 5]
	>>> a
	[1, 2, 1, 4, 3, 5]

<span style="white-space:pre">	</span>>>> list1 = [('david', 90), ('mary',90), ('sara',80),('lily',95)]
	>>> sorted(list1,cmp = lambda x,y: cmp(x[0],y[0]))
	[('david', 90), ('lily', 95), ('mary', 90), ('sara', 80)]
	>>> sorted(list1,cmp = lambda x,y: cmp(x[1],y[1]))
	[('sara', 80), ('david', 90), ('mary', 90), ('lily', 95)]
 

<span style="white-space:pre">	</span>>>> list1 = [('david', 90), ('mary',90), ('sara',80),('lily',95)]
	>>> sorted(list1,key = lambda list1: list1[0])
	[('david', 90), ('lily', 95), ('mary', 90), ('sara', 80)]
	>>> sorted(list1,key = lambda list1: list1[1])
	[('sara', 80), ('david', 90), ('mary', 90), ('lily', 95)]

<span style="white-space:pre">	</span>>>> sorted(list1,reverse = True)
	[('sara', 80), ('mary', 90), ('lily', 95), ('david', 90)]

>>> from operator import itemgetter
>>> sorted(list1, key=itemgetter(1))
[('sara', 80), ('david', 90), ('mary', 90), ('lily', 95)]
>>> sorted(list1, key=itemgetter(0))
[('david', 90), ('lily', 95), ('mary', 90), ('sara', 80)]

<span style="white-space:pre">	</span>>>> import operator
	>>> a = [1,2,3]
	>>> b = operator.itemgetter(0)
	>>> b(a)
	1

>>> sorted(list1, key=itemgetter(0,1))
[('david', 90), ('lily', 95), ('mary', 90), ('sara', 80)]