numpy 有多种排序方法。
sort
sort(self, axis=-1, kind='quicksort', order=None)：排完序后改变原值 【只有这个方法改变原值】
axis : int, optional Axis along which to sort. Default is -1, which means sort along the last axis. kind : {'quicksort', 'mergesort', 'heapsort', 'stable'}, optional Sorting algorithm. Default is 'quicksort'. order : str or list of str, optional When `a` is an array with fields defined, this argument specifies which fields to compare first, second, etc. A single field can be specified as a string, and not all fields need be specified, but unspecified fields will still be used, in the order in which they come up in the dtype, to break ties.
示例
a=np.arange(1,5) print(a) # [1 2 3 4] a.sort() print(a) # [1 2 3 4] b=np.array([[1,5,3],[4,2,7]]) b.sort() print(b) # [[1 3 5] # [2 4 7]] b=np.array([[1,5,3],[4,2,7]]) b.sort(axis=0, kind='quicksort') print(b) # [[1 2 3] # [4 5 7]] # b=np.array([[1,5,3],[4,2,7]]) # b.sort(axis=0,kind='quicksort',order=None) # print(b) # 参数： # axis=0 表示按列 1 表示按行;默认是1按行排序 # kind 排序的算法，提供了快排（quicksort）、混排、堆排
np.sort
sort(a, axis=-1, kind='quicksort', order=None)：用法同 sort，但是不改变原值
c=np.array([[1,5,3],[4,2,7]]) print(np.sort(c)) # [[1 3 5] # [2 4 7]] print(np.sort(c,axis=0)) # [[1 2 3] # [4 5 7]] print(c) # [[1 5 3] 原值没变 # [4 2 7]]
np.argsort
argsort(self, axis=-1, kind='quicksort', order=None)：返回排序后的索引
# 一维数组 data5 = np.array([1, 5, 3]) print data5.argsort() # [0 2 1] 升序 print np.argsort(data5) # [0 2 1] print np.argsort(-data5) # [1 2 0] 降序 # 二维数组 data6 = np.array([[1,2,3],[4,5,6],[0,0,1]]) # [[1 2 3] # [4 5 6] # [0 0 1]] print np.argsort(data6, axis=1) # 按行排序 # [[0 1 2] # [0 1 2] # [0 1 2]] print np.argsort(data6, axis=0) # 按列排序 # [[2 2 2] # [0 0 0] # [1 1 1]] a_arg = np.argsort(data6[:,1]) # 按第'1'列排序 print a_arg # [2 0 1] 第2个排1，第0个排2，第1个排3 a = data6[a_arg] print a # [[0 0 1] # [1 2 3] # [4 5 6]]
