I get it, thanks!

在 2015年12月31日,上午3:00,Michael Armbrust <michael@databricks.com> 写道:

The goal here is to ensure that the non-deterministic value is evaluated only once, so the result won't change for a given row (i.e. when sorting).

On Tue, Dec 29, 2015 at 10:57 PM, 汪洋 <tiandiwoxin@icloud.com> wrote:
Hi fellas,
I am new to spark and I have a newbie question. I am currently reading the source code in spark sql catalyst analyzer. I not quite understand the partial function in PullOutNondeterministric. What does it mean by "pull out”? Why do we have to do the "pulling out”?
I would really appreciate it if somebody explain it to me. 
Thanks.