Q:

How does one merge dataframes by row name without adding a "Row.names" column?

If I have two data frames, such as:
df1 = data.frame(x=1:3,y=1:3,row.names=c('r1','r2','r3'))
df2 = data.frame(z=5:7,row.names=c('r5','r6','r7'))

(
R> df1
   x y
r1 1 1
r2 2 2
r3 3 3

R> df2
   z
r5 5
r6 6
r7 7

), I'd like to merge them by row names, keeping everything (so an outer join, or all=T). This does it:
merged.df <- merge(df1,df2,all=T,by='row.names')
R> merged.df
  Row.names  x  y  z
1        r1  1  1 NA
2        r2  2  2 NA
3        r3  3  3 NA
4        r5 NA NA  5
5        r6 NA NA  6
6        r7 NA NA  7

but I want the input row names to be the row names in the output dataframe (merged.df).
I can do:
rownames(merged.df) <- merged.df[[1]]
merged.df <- merged.df[-1]

which works, but seems inelegant and hard to remember. Anyone know of a cleaner way?

A:

Not sure if it's any easier to remember, but you can do it all in one step using transform.
transform(merge(df1,df2,by=0,all=TRUE), row.names=Row.names, Row.names=NULL)
#    x  y  z
#r1  1  1 NA
#r2  2  2 NA
#r3  3  3 NA
#r5 NA NA  5
#r6 NA NA  6
#r7 NA NA  7

