[R] Finding the neighbors of the point

[Leaf Sun]

Dear all,

I got point data of trees. I was wondering if anybody has experience in searching the neighbors within a specified distance efficiently.

X    Y     Z
99 	34	 65
98 	35	 29
98 	34	 28
99 	33	 33
98 	32	 23
99 	33	 21
99 	33	 22
99 	32	 24
99 	30	 23
    ...

What I want to do is :  searching for the neighbors with a distance R for each tree  & the neighbor must have a bigger  Z.


The data set is huge so the R-codes is working slowly when I search it without subset it. 

Any suggestion would be much appreciated!

Leaf