Dear Julia,
Try this:
DF<-read.table(textConnection("
x1 x2 x3
1 2 3
4 5 6
7 8 9"),header=TRUE)
closeAllConnections()
DF$x4<-DF$x1+DF$x2
DF
HTH,
Jorge
On Tue, Jan 20, 2009 at 2:12 PM, Julia Zhou <ms.juliaz...@gmail.com> wrote:
> Hi,
>
> I would like to operate on certain columns in a dataframe, but not
> others. My data looks like this:
>
> x1 x2 x3
> 1 2 3
> 4 5 6
> 7 8 9
>
> I want to create a new column named x4 that is the sum of x1 and x2,
> but NOT x3. I looked at colSums and apply, but those functions seem to
> use all the columns in a dataframe. How do I only use select columns?
>
> If it helps, in Stata this would be gen x4 = x1 + x2.
>
> Thanks!
>
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