How to keep two Vectors to be

Hi all,

I am beginner of R. I want to ask for help from you. 

I have two "data.frame" type object : s40 and s100. s40 and s100 have same structure: they are actually two dimention array like : 

V1    V2
34     6768
234   36
65     60
.....

Now s40 and s100 have almost same value in V1, but they lack some value in V1 from each other. What I want to do is to expand them to be same long by inserting those lacking values into V1 of s40 and s50 and the responed value in V2 is 0 or mean of V2. 

Is there any easy way to set this problem down? Any help will be appreciated very much!

	Jia Yiyu