curve growth question

[zhu]

I 'm working on crack effects recently.

got my curves  from my fracture pattern , like this:

 

and I want to make it grow in some kind of order ,from top to bottom ,basically.

I can use the carve node and keyframe the second U parameter by using its primitive name separately,

but just curious if there are any  procedural way to do it.

trying to use the carve node in foreach primitive node ,but can't figure out how to carve  each iteration in some order.

 

any advice would be grateful.