Chartjs-How to slice list items in Django Template using javascript (or similar)

I’ve just realized that I cannot use the slice parameter, since it would effectively slice the list.
I didn’t explain it in the first message but my goal is that the user can change the number of columns he wants to see, over and over.
If I slice the list, I can no longer get the sliced data…

Nevertheless, I still want the user to change the number of (last) columns in the graph.

Thanks you all!