R-alpha: ?bug in [.data.frame

[Peter Dalgaard BSA]

Thomas Lumley <thomas@biostat.washington.edu> writes:

> 
> 
> If you subscript a data frame using the names of the columns and there is
> more than one column with the same name only the first one is found.
> eg
> 	mm<-data.frame(1:10,log(1:10))
> 	names(mm)<-c("(offset)","(offset)")
> 	mm[,"(offset)"]			# only returns first column
> 	mm[,"(offset)"]<-rep(1,10)	# only sets first column
> 
> This *is* compatible with S, but I still think it's the wrong thing to do.

This is a generic list thing. Nothing keeps you from having several
elements with the same name, you just get certain problems accessing
them. 

> l<-list(1,2,3)
> names(l)<-c("a","b","b")
> l
$a
[1] 1

$b
[1] 2

$b
[1] 3

> l$b
[1] 2

I rather strongly suspect that coding for the possibility, that in a
list of vectors l$b could mean another list, would be a real pain.
I.e. you deserve what you get...

If you must have identically named columns, try something along the
lines of

> l[names(l)=="b"]
$b
[1] 2

$b
[1] 3

> l[names(l)=="b"]<-4
> l
$a
[1] 1

$b
[1] 4

$b
[1] 4


-- 
   O__  ---- Peter Dalgaard             Blegdamsvej 3  
  c/ /'_ --- Dept. of Biostatistics     2200 Cph. N   
 (*) \(*) -- University of Copenhagen   Denmark      Ph: (+45) 35327918
~~~~~~~~~~ - (p.dalgaard@biostat.ku.dk)             FAX: (+45) 35327907
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