After Effects expression using Index position isn't working between comps and shapes

Question

I have many shapes that I want to reference to a single comp with a shape in it, in case I need to change them later on.

The shapes are 2D and in different positions all over my canvas.

I want to be able to position each comp using the position data from the layer above it.

When I try to map the position data from the layer above, I get the wrong position.

What am I doing wrong?

As a simple example - I want to position the green star in the same place at the pentagon. The pentagon is pre-comped in a 300x300 comp, but everything is centred.

I put this in the star's position field:

x = (index-1);
y = (index-1);
[x,y]

And place the star layer below the pentagon layer.

Why does the star jump to -1,-1?

Answer 1

ah I think i've got it:

x = thisComp.layer(index-1).position[0];
y = thisComp.layer(index-1).position[1];
[x,y]

(I was returning the value of the layer, not the position of that layer)