How to get a new RDD by ordinarily subtract its adjacent rows

[Zhiliang Zhu]

Dear , 

I have took lots of days to think into this issue, however, without any 
success...I shall appreciate your all kind help.
There is an RDD<int> rdd1, I would like get a new RDD<int> rdd2, each row in 
rdd2[ i ] = rdd1[ i ] - rdd[i - 1] .What kinds of API or function would I use...

Thanks very much!John