How can I use expresions only on x dimension if I cant separate 'em ?

[zrils_I_designs]

This is effect called advanced lightning, it has those anchor point-like start and end points, I want to sync the the point going up and down to music. For that I will use the value Im getting from Sound keys effect [Im syncing it to bass]. I'd  be parenting the value I get to anchor point X value, but I can't separate dimensions, what can I do to make this happen ?

[Mylenium]

Position values are arrays and you always can splice out a single value by addressing its array index, in your case simply as value[0] for the X component.

Mylenium

[Kyle Hamrick · Accepted solution]

Yep, as Mylenium said.

Arrays are expressions' way of addressing properties with multiple values. (Here's some good explanation.)

For 2d position, x & y become [0] and [1] in expressions. (For 3d: [0], [1], [2])
While technically not necessary, it's often helpful to use variables to keep track of what you're doing. So, yours might look like:

x=value[0];
y=(pickwhip to appropriate property);
[x,y]

If you wanted to retain control over the Y value, but have it also be affected by another property, you could do something like:

x=value[0];

y=value[1]+(pickwhip to appropriate property);

[x,y]

In that second case, it'll be linked to the Sound Keys property, but you'd also be able to keyframe the Direction independently of the expression. Whether you use +, -, *, /, etc. is up to you.

[zrils_I_designs]

Thank you! Just needed to not be as stupid as I was, that cleared out a lot for me. It works !

[Andrew Yoole]

Dan Ebberts is the grandfather of After Effects Expressions.  His site is great for learning some of the basics and useful tricks:

MotionScript.com - main page

[Kyle Hamrick]

Heh. Nothing stupid about the question. It's hardly the most intuitive thing.