R help - May 2011 - Change the names of a dataframe

Dear list,

This may sound silly. What is the right way to change the names of a
dataframe? Let's say I have this data frame (dose) with four columns with
names "ID", "DOSE", "TIME" "CMT". I want
to change "DOSE" to "AMT". So I did

names(dose[2])<-'AMT'

But nothing happened. The name of the second column is still "DOSE".

Only this works

names(dose)[2]<-'AMT'

I wonder what is wrong with the first method. Thanks.

Jun

	[[alternative HTML version deleted]]

In the first case you create a new data frame consisting of the 2nd column of
the original, then change the name of the only column in that new data frame,
then since nothing is done with that data frame it gets thrown away.  So it is
not that nothing happened, but just that nothing useful happened.  The original
data frame was never changed, just a copy of it.

The second method access the names, then changes the 2nd name and therefore
changes the actual data frame of interest.

-- 
Gregory (Greg) L. Snow Ph.D.
Statistical Data Center
Intermountain Healthcare
greg.snow at imail.org
801.408.8111

> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-
> project.org] On Behalf Of Jun Shen
> Sent: Tuesday, May 03, 2011 2:43 PM
> To: R-help
> Subject: [R] Change the names of a dataframe
> 
> Dear list,
> 
> This may sound silly. What is the right way to change the names of a
> dataframe? Let's say I have this data frame (dose) with four columns
> with
> names "ID", "DOSE", "TIME" "CMT". I
want to change "DOSE" to "AMT". So
> I did
> 
> names(dose[2])<-'AMT'
> 
> But nothing happened. The name of the second column is still
"DOSE".
> 
> Only this works
> 
> names(dose)[2]<-'AMT'
> 
> I wonder what is wrong with the first method. Thanks.
> 
> Jun
> 
> 	[[alternative HTML version deleted]]
> 
> ______________________________________________
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> PLEASE do read the posting guide http://www.R-project.org/posting-
> guide.html
> and provide commented, minimal, self-contained, reproducible code.

On 03/05/2011 4:43 PM, Jun Shen wrote:
> Dear list,
>
> This may sound silly. What is the right way to change the names of a
> dataframe? Let's say I have this data frame (dose) with four columns
with
> names "ID", "DOSE", "TIME" "CMT". I
want to change "DOSE" to "AMT". So I did
>
> names(dose[2])<-'AMT'
>
> But nothing happened. The name of the second column is still
"DOSE".
>
> Only this works
>
> names(dose)[2]<-'AMT'
>
> I wonder what is wrong with the first method. Thanks.
>
The first method says:

1.  Get dose[2].  This is a dataframe consisting of the second column of 
dose.  Store it in a temporary, unnamed variable.

2.  Changes its names to 'AMT'. This changes the names of the temporary 
variable, which then disappears.

The second method says:

1. Set the second element of the names associated with dose to 'AMT'.

That's what you want to do.

Duncan Murdoch