[R] Merge two dataframe with "by", and problems with the common field

[William Dunlap]

> If the "a" columns are distinct, then at least one of them needs a new name in the
> merged table, and the simplest option is to rename the columns appropriately in d1 and
> d2 (since they apparently represent different data anyway).

You can also use the 'suffixes. argument to merge to control the naming of the
common column names that are not used as 'by' columns:
  > merge(d1,d2,by="b", suffixes=c("", ".y"))
    b a c d a.y  f
  1 4 1 5 6   1  8
  2 5 2 6 7   2  9
  3 6 3 7 8   3 10

Bill Dunlap
Spotfire, TIBCO Software
wdunlap tibco.com


> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] On Behalf
> Of Jeff Newmiller
> Sent: Tuesday, May 07, 2013 12:10 AM
> To: jpm miao; r-help
> Subject: Re: [R] Merge two dataframe with "by", and problems with the common field
> 
> Either d1$a and d2$a are always the same, or they are not.
> 
> If they are already the same, you can either omit one of them in the merge:
> 
> merge(d1, d2[,-2], by="b")
> 
> or you can use a set of columns for your by:
> 
> merge(d1,d2, by=c("a","b"))
> 
> If the "a" columns are distinct, then at least one of them needs a new name in the
> merged table, and the simplest option is to rename the columns appropriately in d1 and
> d2 (since they apparently represent different data anyway).
> ---------------------------------------------------------------------------
> Jeff Newmiller                        The     .....       .....  Go Live...
> DCN:<jdnewmil at dcn.davis.ca.us>        Basics: ##.#.       ##.#.  Live Go...
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> Sent from my phone. Please excuse my brevity.
> 
> jpm miao <miaojpm at gmail.com> wrote:
> 
> >Hi,
> >
> > From time to time I merge two dataframes with possibly a common field.
> >Then the common field is no longer present,but what are present
> >fieldname.x
> >and fieldname.y. How can I fix the problem so that I can still call by
> >the
> >orignal fieldname? If you don't understand my problem, please see the
> >example below.
> >
> >   Thanks
> >
> >Miao
> >
> >
> >> d1
> >  a b c
> >1 1 4 5
> >2 2 5 6
> >3 3 6 7
> >> d2
> >  d a  f b
> >1 6 1  8 4
> >2 7 2  9 5
> >3 8 3 10 6
> >> d3<-merge(d1, d2, by="b")
> >> d3
> >  b a.x c d a.y  f
> >1 4   1 5 6   1  8
> >2 5   2 6 7   2  9
> >3 6   3 7 8   3 10
> >> d3["a"]
> >Error in `[.data.frame`(d3, "a") : undefined columns selected
> >> d3["a.x"]
> >  a.x
> >1   1
> >2   2
> >3   3
> >
> >	[[alternative HTML version deleted]]
> >
> >______________________________________________
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> 
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