R help - Jul 2010 - select columns from vector of column names

Hi

I want to extract columns from a data frame using a vector with the desired
column names.

This short example uses the select argument in the subset function to
accomplish what I am trying to do.  Is there a better solution?

#names of desired columns
colnames <- c("col1","col3")

#my data
data <-
data.frame("col1"=c(1,2,3),"col2"=c("A","B","C"),"col3"=c(4,5,6))

fun <- function(colname,dframe){
nframe <- subset(dframe,select=colname)
    vec <- nframe[,1]
    return(vec)
}

fun(colnames[1],data)
fun(colnames[2],data)

	[[alternative HTML version deleted]]

How about

data[,colnames(data)%in%colnames] 


-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org]
On Behalf Of Jonathan Flowers
Sent: Friday, July 09, 2010 11:27 AM
To: r-help at r-project.org
Subject: [R] select columns from vector of column names

Hi

I want to extract columns from a data frame using a vector with the desired
column names.

This short example uses the select argument in the subset function to
accomplish what I am trying to do.  Is there a better solution?

#names of desired columns
colnames <- c("col1","col3")

#my data
data <-
data.frame("col1"=c(1,2,3),"col2"=c("A","B","C"),"col3"=c(4,5,6))

fun <- function(colname,dframe){
nframe <- subset(dframe,select=colname)
    vec <- nframe[,1]
    return(vec)
}

fun(colnames[1],data)
fun(colnames[2],data)

	[[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.

How about

  data[ , colnames]
Or
  data[ , colnames[1]]
  data[ , colnames[2]]

-Don


On 7/9/10 11:27 AM, "Jonathan Flowers" <jonathanmflowers at
gmail.com> wrote:
> Hi
> 
> I want to extract columns from a data frame using a vector with the desired
> column names.
> 
> This short example uses the select argument in the subset function to
> accomplish what I am trying to do.  Is there a better solution?
> 
> #names of desired columns
> colnames <- c("col1","col3")
> 
> #my data
> data <-
data.frame("col1"=c(1,2,3),"col2"=c("A","B","C"),"col3"=c(4,5,6))
> 
> fun <- function(colname,dframe){
> nframe <- subset(dframe,select=colname)
>     vec <- nframe[,1]
>     return(vec)
> }
> 
> fun(colnames[1],data)
> fun(colnames[2],data)
> 
> [[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.
> 
-- 
Don MacQueen
Environmental Protection Department
Lawrence Livermore National Laboratory
925 423-1062