mrip mrip - 3 months ago 38
R Question

Simplest way to get rbind to ignore column names

This came up just in an answer to another question here. When you

rbind
two data frames, it matches columns by name rather than index, which can lead to unexpected behavior:

> df<-data.frame(x=1:2,y=3:4)
> df
x y
1 1 3
2 2 4
> rbind(df,df[,2:1])
x y
1 1 3
2 2 4
3 1 3
4 2 4


Of course, there are workarounds. For example:

rbind(df,rename(df[,2:1],names(df)))
data.frame(rbind(as.matrix(df),as.matrix(df[,2:1])))


On edit:
rename
from the
plyr
package doesn't actually work this way (although I thought I had it working when I originally wrote this...). The way to do this by renaming is to use SimonO101's solution:

rbind(df,setNames(df[,2:1],names(df)))


Also, maybe surprisingly,

data.frame(rbindlist(list(df,df[,2:1])))


works by index (and if we don't mind a data table, then it's pretty concise), so this is a difference between
do.call(rbind)
.

The question is, what is the most concise way to
rbind
two data frames where the names don't match? I know this seems trivial, but this kind of thing can end up cluttering code. And I don't want to have to write a new function called
rbindByIndex
. Ideally it would be something like
rbind(df,df[,2:1],byIndex=T)
.

Answer

You might find setNames handy here...

rbind(df, setNames(rev(df), names(df)))
#  x y
#1 1 3
#2 2 4
#3 3 1
#4 4 2

I suspect your real use-case is somewhat more complex. You can of course reorder columns in the first argument of setNames as you wish, just use names(df) in the second argument, so that the names of the reordered columns match the original.

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