I have the following list or numpy array

```
  ll=[7.2,0,0,0,0,0,6.5,0,0,-8.1,0,0,0,0]

```

and an additional list indicating the positions of non-zeros

```
  i=[0,6,9]

```

I would like to make two new lists out of them, one filling the zeros and one counting in between, for this short example:

```
  a=[7.2,7.2,7.2,7.2,7.2,7.2,6.5,6.5,6.5,-8.1,-8.1,-8.1,-8.1,-8.1]
  b=[0,1,2,3,4,5,0,1,2,0,1,2,3,4]

```

Is therea a way to do that without a for loop to speed up things, as the list ll is quite long in my case.