Well, there is always the online help. If you try to delete a size zero, i'd expect that you won't get anything.
😉 Also don't forget to initialize the shift register on the left.
Delete from array is very inefficient to get a row, in your case you get a 0x0 2D array which you append into a 3D array, blowing everything out of proportion.
To get a single row of a 2D array, use index array with one index disconnected.
However, this seems a bit too convoluted to do this simple task. Why don't you just simply only pick every third element to store in the second array, such as in the code of the attached picture.
In general, it is not a good idea to grow arrays indefinitely, you'll eventually run
out of memory. You should rethink your design, e.g. use a fixed size 2D array which keeps the last 100 values only.