R help - Oct 2013 - quote a column of a dataframe by its name

Dear All,

I have a question, suppose X is a dataframe, with column names as
"x1", "x2", "x3", ..... And I would like to use
the i-th column by X[,'xi'].
But it seems the single quote and double quote are different.
So if I run X[, names(X)[i]], it has some error.
Please use the below example code

X = matrix(rnorm(50),ncol = 5)
X = data.frame(X)
names(X)=c("x1","x2","x3","x4","x5")

#pick the 4-th column
X[,'x4']  #working
X[,names(X)[4]]  # not working , so how to modify this line?

names(X)[4] #  returns "x4"
sQuote(names(X)[4])  # returns "'x4'"


Best,

Sorry, this sample code seems to be OK.
I will look into my original problem and update it soon.

Best wishes,


On Fri, Oct 4, 2013 at 12:06 PM, Jie <jimmycloud at gmail.com>
wrote:
> Dear All,
>
> I have a question, suppose X is a dataframe, with column names as
> "x1", "x2", "x3", ..... And I would like to
use the i-th column by X[,'xi'].
> But it seems the single quote and double quote are different.
> So if I run X[, names(X)[i]], it has some error.
> Please use the below example code
>
> X = matrix(rnorm(50),ncol = 5)
> X = data.frame(X)
>
names(X)=c("x1","x2","x3","x4","x5")
>
> #pick the 4-th column
> X[,'x4']  #working
> X[,names(X)[4]]  # not working , so how to modify this line?
>
> names(X)[4] #  returns "x4"
> sQuote(names(X)[4])  # returns "'x4'"
>
>
> Best,

Hello,

I had no problems, and it shouldn't. What exactly do you mean by "not 
working"?

Hope this helps,

Rui Barradas

Em 04-10-2013 17:06, Jie escreveu:
> Dear All,
>
> I have a question, suppose X is a dataframe, with column names as
> "x1", "x2", "x3", ..... And I would like to
use the i-th column by X[,'xi'].
> But it seems the single quote and double quote are different.
> So if I run X[, names(X)[i]], it has some error.
> Please use the below example code
>
> X = matrix(rnorm(50),ncol = 5)
> X = data.frame(X)
>
names(X)=c("x1","x2","x3","x4","x5")
>
> #pick the 4-th column
> X[,'x4']  #working
> X[,names(X)[4]]  # not working , so how to modify this line?
>
> names(X)[4] #  returns "x4"
> sQuote(names(X)[4])  # returns "'x4'"
>
>
> Best,
>
> ______________________________________________
> 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.
>

X[,names(X)[4]]  works fine  for me.  I had never thought of doing this. Neat
idea.

John Kane
Kingston ON Canada

> -----Original Message-----
> From: jimmycloud at gmail.com
> Sent: Fri, 4 Oct 2013 12:06:50 -0400
> To: r-help at r-project.org
> Subject: [R] quote a column of a dataframe by its name
> 
> Dear All,
> 
> I have a question, suppose X is a dataframe, with column names as
> "x1", "x2", "x3", ..... And I would like to
use the i-th column by
> X[,'xi'].
> But it seems the single quote and double quote are different.
> So if I run X[, names(X)[i]], it has some error.
> Please use the below example code
> 
> X = matrix(rnorm(50),ncol = 5)
> X = data.frame(X)
>
names(X)=c("x1","x2","x3","x4","x5")
> 
> #pick the 4-th column
> X[,'x4']  #working
> X[,names(X)[4]]  # not working , so how to modify this line?
> 
> names(X)[4] #  returns "x4"
> sQuote(names(X)[4])  # returns "'x4'"
> 
> 
> Best,
> 
> ______________________________________________
> 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.
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