[R] help with merging 2 data frames

[Mercier Eloi]

This should do the trick :

colnames(y)[1:2]=c("a","a")
y2=rbind(y[,-1], y[,-2]) #duplicating the "y" matrix so the identifiers 
are only in 1 column
merged = merge(x,y2)

merged
    a b  d  e1  e2
1 aa 1 10 100 101
2 aa 2 20 200 201
3 ab 1 30 100 101
4 ab 2 40 200 201
5 ba 1 50 300 301
6 ba 2 60 400 401
7 bb 1 70 300 301
8 bb 2 80 400 401

desired
    a b  d  e1  e2
1 aa 1 10 100 101
2 aa 2 20 200 201
3 ab 1 30 100 101
4 ab 2 40 200 201
5 ba 1 50 300 301
6 ba 2 60 400 401
7 bb 1 70 300 301
8 bb 2 80 400 401

  all(merged==desired)
[1] TRUE

Cheers,

Eloi

On 12-07-11 03:50 PM, Dimitri Liakhovitski wrote:
> Jorge, thank you!
> that seems to be working, but unfortunately in real life I have
> thousands of variables (except for a, a2, a3 and b) so that manually
> selecting columns (as in c(2:4, 8:9)) would be too difficult...
> Dimitri
>
> On Wed, Jul 11, 2012 at 6:36 PM, Jorge I Velez <jorgeivanvelez at gmail.com> wrote:
>> Hi Dimitri,
>>
>> Try creating a key for "x" and "y" and then merging the result by that
>> variable:
>>
>> x$key <- with(x, paste(a, b, sep = "/"))
>> y$key <- with(y, paste(a2, b, sep = "/"))
>> merge(x, y, by = 'key')[, c(2:4, 8:9)]
>>
>> HTH,
>> Jorge.-
>>
>>
>> On Wed, Jul 11, 2012 at 6:28 PM, Dimitri Liakhovitski <> wrote:
>>> 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)
>>>
>>> --
>>> Dimitri Liakhovitski
>>> marketfusionanalytics.com
>>>
>>> ______________________________________________
>>> R-help at r-project.org mailing list
>>> https://stat.ethz.ch/mailman/listinfo/r-help
>>> PLEASE do read the posting guide
>>> http://www.R-project.org/posting-guide.html
>>> and provide commented, minimal, self-contained, reproducible code.
>>
>
>


-- 
Eloi Mercier
Bioinformatics PhD Student, UBC
Paul Pavlidis Lab
2185 East Mall
University of British Columbia
Vancouver BC V6T1Z4