Slicing in 3D array

#1

for img = np.arange(333).reshape(3,3,3)
can someone please explain the meaning of img[:, ::-1] step wise?

#2

hey @nikhil_0406 ,
when we just do array[:] , it means we want to access all the components.
So taking the current case ,
we have an array of shape (2,3,4) , we can say it as a bunch of 2 arrays each of shape ( 3,4 ) concatenated vertically.

So , on doing img[:,something here] will mean that , we need to perform some operation on each array in this full array , means performing same operation on both ( 3,4 ) shape arrays.
and you know that ::-1 is a special operation to reverse.
so currently the first array inside this big array is

[[ 0 1 2 3] [ 4 5 6 7] [ 8 9 10 11]]

which means on applying the reverse operation it gets changed as

[[ 8 9 10 11] [ 4 5 6 7] [ 0 1 2 3]]

simply a reversion on indexs [1,2,3] to [3,2,1].

The same thing happen with the other array also and in this way this array gets internally reversed.

I hope this helps.
Thank You and Happy Learning :slightly_smiling_face:.

1 Like
#3

::-1 is a special operation to reverse. I learned today, thankyou.

#5

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