[R] Bug in colnames of data.frames?

[Uwe Ligges]

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" ]

This bug is the user ... ;-)

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

Aha! You have created a data.frame consisting of one column! What you 
mean really mean is
  myData$var5 <- myData[[ "var1" ]] + myData[[ "var2" ]]

Uwe Ligges





> 
> 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
> 
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