R help - Jun 2013 - pasting columns of a dataframe together

I want  to "paste" the contents of the first column of a dataframe
with all the columns of the same dataframe.



What is a "good" way to do this, perhaps something more elegant than
what I have below.  (My actual dataframe has ~400 columns and ~35000
rows.)



example1:

mydf <- data.frame( matrix(data=1:15, nrow=5, ncol=3) )

mydf2 <- mydf

temp2 <- paste(unlist(mydf[,1]) , unlist(mydf), sep="_")

mydf2[ ,] <- temp2



example2:

mydf2 <- mydf



for(i in 1:ncol(mydf2) ) {

mydf2[i] <- paste( mydf[,1], mydf[ ,i], sep='_')

}

Given the size of my dataframe (>400 columns, >35000 rows), I should
have clarified that speed and efficiency is perhaps as important as
"elegance", and I'd like to use the examples to learn about any
corrections and improvements I can make in the examples I provided.
Thanks for any help you can offer. (I am using R x64 2.15.2 on Windows
7.)

On Wed, Jun 26, 2013 at 3:14 PM, Anika Masters <anika.masters at
gmail.com> wrote:
> I want  to "paste" the contents of the first column of a
dataframe
> with all the columns of the same dataframe.
>
>
>
> What is a "good" way to do this, perhaps something more elegant
than
> what I have below.  (My actual dataframe has ~400 columns and ~35000
> rows.)
>
>
>
> example1:
>
> mydf <- data.frame( matrix(data=1:15, nrow=5, ncol=3) )
>
> mydf2 <- mydf
>
> temp2 <- paste(unlist(mydf[,1]) , unlist(mydf), sep="_")
>
> mydf2[ ,] <- temp2
>
>
>
> example2:
>
> mydf2 <- mydf
>
>
>
> for(i in 1:ncol(mydf2) ) {
>
> mydf2[i] <- paste( mydf[,1], mydf[ ,i], sep='_')
>
> }