R help - Jan 2009 - Summing Select Columns of a Data Frame?

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!

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.juliazhou@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!
>
> ______________________________________________
> R-help@r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>
	[[alternative HTML version deleted]]

Hi Julia,

or you can use colSums on an appropriate sub-data.frame:

colSums(dataset[,c(1,2)])

HTH,
Stephan


Jorge Ivan Velez schrieb:
> 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.juliazhou at
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!
>>
>> ______________________________________________
>> R-help at r-project.org mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-help
>> PLEASE do read the posting guide
>> http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>>
> 
> 	[[alternative HTML version deleted]]
> 
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>