Path Switch (Behind The Scenes)
I thought I'd render this out with the nulls included to hopefully show a little more detail about what the expression achieves. Notice how the balls switch between the nulls, this is controlled using a slider with the expression below.
Expression:
path = thisComp.layer("Controller").effect("Path Switch")("Slider");
a = thisComp.layer("Path 03").toWorld ([60,60,0]);
b = thisComp.layer("Path 01").toWorld ([60,60,0]);
c = thisComp.layer("Path 04").toWorld ([60,60,0]);
d = thisComp.layer("Path 02").toWorld ([60,60,0]);
if(path <= 25){
linear (path, 0, 25, a, b);
} else if (path >= 25 && path <= 50) {
linear (path, 25, 50, b, c);
} else if (path >= 50 && path <= 75) {
linear (path, 50, 75, c, d);
} else if (path >= 75 && path <= 100) {
linear (path, 75, 100, d, a)
}