Numpy 数组的切片操作

实例+解释如下（表格）：关键是要明白python中数组的下标体系。一套从左往右，一套从右往左。

 1 import numpy as np
 2 import sys
 3
 4 def main():
 5     A=np.array([1,2,3,4,5,6,7,8,9,0])
 6     B=A.copy()
 7     print A
 8     print ‘same as print A,‘,A[:]
 9     print ‘same as print A,‘,A[::1]
10     print ‘reverse A,‘,A[::-1]
11     print ‘print all elements with 2 interval,‘,A[::2]
12     print ‘print elements from the 4th element with 2 interval,‘,A[3::2]
13     print ‘print elements from the last 4th element with 2 interval,‘,A[-3::2]
14     print ‘print elements from the 2nd to 5th element with 2 interval,‘,A[1:4:2]
15     print ‘reverse print all elements with 2 interval,‘,A[::-2]
16     print ‘reverse print elements from the 4th element with 2 interval,‘,A[3::-2]
17     print ‘reverse print elements from the last 4th element with 2 interval,‘,A[-3::-2]
18     #print A[a:b:c]: a and b determine range of slide. c determine the interval and direction (forth or reverse)
19     print A[:-3:-1]
20     print A[:3:1]
21     print A[:3:-1]
22     C=A[::-1]
23     C[0]=10
24     print ‘A is also changed as how does c change,‘,A
25     B[9]=0
26     print ‘A will not be affected when B change,‘,A
27     print ‘array slide from second element to the last one,‘,A[1:]
28     print ‘array slide from last second element to the first one,‘,A[:-1]
29
30
31
32 if __name__ == "__main__":
33     main()