[R] help with merging 2 data frames

[Rui Barradas]

Hello,

About many columns like 'e1' and 'e2' I don't know but with the provided 
example the following does NOT depend on them, only on 'a', 'b' and 'a2' 
and 'a3'.


z <- lapply(c("a2", "a3"), function(cc) merge(x, y, by.x=c("a", "b"), 
by.y=c(cc, "b")))
z <- lapply(seq_along(z), function(i)
         z[[i]][ -which(names(z[[i]]) %in% c("a2", "a3")) ])
z <- do.call(rbind, z)
z <- z[order(z$a, z$b), ]
rownames(z) <- seq_len(nrow(z))
all.equal(desired, z)


Hope this helps,

Rui Barradas

Em 11-07-2012 23:28, Dimitri Liakhovitski escreveu:
> Dear R-ers,
>
> I feel I am close, but can't get it quite right.
> Thanks a lot for your help!
>
> Dimitri
>
> # I have 2 data frames:
>
> x<-data.frame(a=c("aa","aa","ab","ab","ba","ba","bb","bb"),b=c(1:2,1:2,1:2,1:2),d=c(10,20,30,40,50,60,70,80))
> y<-data.frame(a2=c("aa","aa","ba","ba"),a3=c("ab","ab","bb","bb"),b=c(1:2,1:2),e1=c(100,200,300,400),e2=c(101,201,301,401))
> (x);(y)
>
> # I'd like to merge them so that the result looks like this:
>
> desired<-data.frame(a=c("aa","aa","ab","ab","ba","ba","bb","bb"),b=c(1:2,1:2,1:2,1:2),d=c(10,20,30,40,50,60,70,80),
> 	e1=c(100,200,100,200,300,400,300,400),e2=c(101,201,101,201,301,401,301,401))
> (desired)
>
> # In other words, I want column e1 and e2 entries from data frame y to
> be repeated based on matching of column a from x and columns a2 and
> then a3 from y.
>
> # I am trying step-by-step - first I am using column a2 from data
> frame y for merging:
> out1<-merge(x,y[-2],by.x=c("a","b"),by.y=c("a2","b"),all.x=T,all.y=F)
> (out1)   # looking good - half of the job is done
>
> # Step2 - does not work
>
> # next line produces columns e1 and e2 twice (in real life I have tons
> of columns like e1 and e2):
> merge(out1,y[-1],by.x=c("a","b"),by.y=c("a3","b"),all.x=T,all.y=F)
>
> # next line also doesn't do the job:
> merge(out1,y[-1],by.x=c("a","b","e1","e2"),by.y=c("a3","b","e1","e2"),all.x=T,all.y=F)
>
> # Finally, I tried this approach:
> out1<-merge(x,y[-2],by.x=c("a","b"),by.y=c("a2","b"),all.x=T,all.y=F)
> out2<-merge(x,y[-1],by.x=c("a","b"),by.y=c("a3","b"),all.x=T,all.y=F)
> (out1); (out2)
>
> # Now I need to merge these 2 - however, the next line doubles the
> number of entries:
> merge(out1,out2,by=names(out1),all.x=T,all.y=T)
>