Slicing operations on Numpy arrays

Examples + explanations are as follows (table): The key is to understand the subscript system of arrays in Python. Set from left to right, set from right to left.

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A=np.array ([1,2,3,4,5,6,7,8,9,0])	1	2	3	4	5	6	7	8	9	0
subscript one index (left-to-right)	1	2	3	4	5	6	7	8	9
subscript two index (right-to-left)	-9	-8	-7	-6	-5	-4	-3	-2	-1
A[A:B:C]	A and B determine: The range of the slice operation (from A to B, exclude B), C determines the pace and direction of the specific slice (for example: 1 indicates left to right,pace=1. -1 means right to left,pace=1.).
Example: A[:3:1]	output:1,2,3. Note: The corresponding array value at Index 3 is 4. 1 indicates that the size of the step is 1 from left to right. So output
Example: A[:-3:-1]	output:0,9 Note: The corresponding array value at INDEX-3 is 8. 1 means the size of the step is 1 from right to left. So the output 0,9
Example: A[:3:-1]	output:0,9,8,7,6,5 Note: The corresponding array value at Index 3 is 4. 1 means the size of the step is 1 from right to left. So the output 0,9,8,7,6,5
Example: A[:-3:1]	output:0,9 Note: The corresponding array value at INDEX-3 is 8. 1 indicates that the size of the step is 1 from left to right. So the output 1,2,3,4,5,6,7,8
Example: A[-3::-1]	output:8,7,6,5,4,3,2,1 Note: The corresponding array value at INDEX-3 is 8. 1 means the size of the step is 1 from right to left. So the output 8,7,6,5,4,3,2,1

1 ImportNumPy as NP2 ImportSYS3 4 defMain ():5A=np.array ([1,2,3,4,5,6,7,8,9, 0])6b=a.copy ()7     PrintA8     Print 'Same as print A,', a[:]9     Print 'Same as print A,', A[::1]Ten     Print 'Reverse A,', a[::-1] One     Print 'Print all elements with 2 interval,', A[::2] A     Print 'print elements from the 4th element with 2 interval,', A[3::2] -     Print 'print elements from the last 4th element with 2 interval,', A[-3::2] -     Print 'print elements from the 2nd to 5th element with 2 interval,', A[1:4:2] the     Print 'reverse Print all elements with 2 interval,', a[::-2] -     Print 'Reverse print elements from the 4th element with 2 interval,', a[3::-2] -     Print 'Reverse print elements from the last 4th element with 2 interval,', a[-3::-2] -     #print A[a:b:c]: A and b determine range of slide. C Determine the interval and direction (forth or reverse) +     PrintA[:-3:-1] -     PrintA[:3:1] +     PrintA[:3:-1] AC=a[::-1] atc[0]=10 -     Print 'A is also changed as how to does C change,', A -b[9]=0 -     Print 'A won't is affected when B change,', A -     Print 'array slide from second element to the last one,', a[1:] -     Print 'array slide from last second element to the first one,', a[:-1] in  -  to  + if __name__=="__main__": -Main ()

Slicing operations on Numpy arrays