[R] Merge data frame and keep unmatched

[Marc Schwartz]

On Jun 10, 2009, at 8:56 AM, Etienne B. Racine wrote:

>
> Hi,
>
> With two data sets, one complete and another one partial, I would  
> like to
> merge them and keep the unmatched lines. The problem is that merge()  
> dosen't
> keep the unmatched lines. Is there another function that I could use  
> to
> merge the data frames.
>
> Example:
>
> completedf <- expand.grid(alpha=letters[1:3],beta=1:3)
> partdf <- data.frame(
> 	alpha= c('a','a','c'),
> 	beta = c(1,3,2),
> 	val = c(2,6,4))
>
> mergedf <- merge(x=completedf, y=partdf, by=c('alpha','beta'))
> # it only kept the common rows
> nrow(mergedf)
>
> Thanks,
> Etienne



Is this what you want?

 > merge(x=completedf, y=partdf, by=c('alpha','beta'), all = TRUE)
   alpha beta val
1     a    1   2
2     a    2  NA
3     a    3   6
4     b    1  NA
5     b    2  NA
6     b    3  NA
7     c    1  NA
8     c    2   4
9     c    3  NA

Note the 'all', 'all.x' and 'all.y' arguments...

HTH,

Marc Schwartz