[R] Match data.frames with different number of rows

[Bernd Weiss]

Dear all,

I have two data.frames a and b:

i <- c(1,1,2,2,3,3,4,4)
x <- c(1,53,7,3,4,23,6,2)
a <- data.frame(i,x)

and 

j <- c(1,2,3,4)
y <- c(99,88,77,66)
b <- data.frame(j,y)

So, a looks like this

> a
  i  x
 1  1
 1 53
 2  7
 2  3
 3  4
 3 23
 4  6
 4  2

and b like this

> b
  j  y
 1 99
 2 88
 3 77
 4 66

Now, I would like to match 'b' to 'a', so that a new data.frame 'c' is

> c
  i  x	z
1 1  1	99
2 1 53	99
3 2  7	88	
4 2  3	88
5 3  4	77	
6 3 23	77
7 4  6	66
8 4  2	66

I habe absolutely no idea how to do this. I searched the net, the FAQ, the manuals, my 
four books...

Any help would be appreciated!

Bernd