[R] Bug in colnames of data.frames?

[Marc Schwartz]

On Tue, 2004-08-17 at 09:01, Arne Henningsen wrote:
> Hi,
> 
> I am using R 1.9.1 on on i686 PC with SuSE Linux 9.0.
> 
> I have a data.frame, e.g.:
> 
> > myData <- data.frame( var1 = c( 1:4 ), var2 = c (5:8 ) )
> 
> If I add a new column by
> 
> > myData$var3 <- myData[ , "var1" ] + myData[ , "var2" ]
> 
> everything is fine, but if I omit the commas:
> 
> > myData$var4 <- myData[ "var1" ] + myData[ "var2" ]
> 
> the name shown above the 4th column is not "var4":
> 
> > myData
>   var1 var2 var3 var1
> 1    1    5    6    6
> 2    2    6    8    8
> 3    3    7   10   10
> 4    4    8   12   12
> 
> but names() and colnames() return the expected name:
> 
> > names( myData )
> [1] "var1" "var2" "var3" "var4"
> > colnames( myData )
> [1] "var1" "var2" "var3" "var4"
> 
> And it is even worse: I am not able to change the name shown above the 4th 
> column:
> > names( myData )[ 4 ] <- "var5"
> > myData
>   var1 var2 var3 var1
> 1    1    5    6    6
> 2    2    6    8    8
> 3    3    7   10   10
> 4    4    8   12   12
> 
> I guess that this is a bug, isn't it?
> 
> Arne


Here is a hint:

# This returns an integer vector
> str(myData[ , "var1" ] + myData[ , "var2" ])
 int [1:4] 6 8 10 12


# This returns a data.frame
> str(myData[ "var1" ] + myData[ "var2" ])
`data.frame':	4 obs. of  1 variable:
 $ var1: int  6 8 10 12


> str(myData)
`data.frame':	4 obs. of  5 variables:
 $ var1: int  1 2 3 4
 $ var2: int  5 6 7 8
 $ var3: int  6 8 10 12
 $ var4:`data.frame':	4 obs. of  1 variable:
  ..$ var1: int  6 8 10 12


Take a look at the details, value and coercion sections of ?.data.frame

HTH,

Marc Schwartz