[R] paired samples, matching rows, merge()

[Gabor Grothendieck]

On Fri, Aug 20, 2010 at 6:44 AM, Cecilia Carmo <cecilia.carmo at ua.pt> wrote:
> Hi everyone!
>
> I'm matching two samples to create one sample that have
> pairs of observations equal for the k1 variable. Merge() doesn't work
> because I dont't want to recycle the values.
>
> x <- data.frame(k1=c(1,1,2,3,3,5), k2=c(20,21,22,23,24,25))
> x
> y <- data.frame(k1=c(1,1,2,2,3,4,5,5), k2=c(10,11,12,13,14,15,16,17))
> y
> merge(x,y,by="k1")
>  k1 k2.x k2.y
> 1   1   20   10
> 2   1   20   11
> 3   1   21   10
> 4   1   21   11
> 5   2   22   12
> 6   2   22   13
> 7   3   23   14
> 8   3   24   14
> 9   5   25   16
> 10  5   25   17
>
> I have a final dataframe with 10 rows, but I want it with 5 rows, like this:
>  k1 k2.x k2.y
> 1   1   20   10
> 2   1   21   11
> 3   2   22   12
> 4   3   23   14
> 5   5   25   16
>

Try this:

x$k3 <- with(x, ave(k1, k1, FUN = seq_along))
y$k3 <- with(y, ave(k1, k1, FUN = seq_along))

merge(x, y, by = c("k1", "k3"))