R help - Jul 2005 - Prefix for colnames

Hi,

I would like to add a prefix to colnames in a matrix but I can't get the
prefix
option in colnames to work. What am I doing wrong?
> X<-matrix(NA,3,4)
>
colnames(X)<-c("test","test","test","test")
> colnames(X)<-colnames(X,prefix="PREFIX.")
> X
     test test test test
[1,]   NA   NA   NA   NA
[2,]   NA   NA   NA   NA
[3,]   NA   NA   NA   NA

?? I also tried with do.NULL set to FALSE but it still does not work.

Thank you very much for your help!

Best,
Jens

On 7/20/2005 9:54 AM, jhainm at fas.harvard.edu wrote:
> Hi,
> 
> I would like to add a prefix to colnames in a matrix but I can't get
the prefix
> option in colnames to work. What am I doing wrong?
The prefix argument is only used when there are no names and colnames is 
generating some.  You just want to use paste().
> 
>> X<-matrix(NA,3,4)
>>
colnames(X)<-c("test","test","test","test")
 > colnames(X) <- paste("PREFIX.", colnames(X),
sep="")
 > X
      PREFIX.test PREFIX.test PREFIX.test PREFIX.test
[1,]          NA          NA          NA          NA
[2,]          NA          NA          NA          NA
[3,]          NA          NA          NA          NA

Duncan Murdoch

jhainm at fas.harvard.edu writes:
> Hi,
> 
> I would like to add a prefix to colnames in a matrix but I can't get
the prefix
> option in colnames to work. What am I doing wrong?
> 
> > X<-matrix(NA,3,4)
> >
colnames(X)<-c("test","test","test","test")
> > colnames(X)<-colnames(X,prefix="PREFIX.")
> > X
>      test test test test
> [1,]   NA   NA   NA   NA
> [2,]   NA   NA   NA   NA
> [3,]   NA   NA   NA   NA
> 
> ?? I also tried with do.NULL set to FALSE but it still does not work.
> 
> Thank you very much for your help!
Well
> colnames
function (x, do.NULL = TRUE, prefix = "col")
{
    dn <- dimnames(x)
    if (!is.null(dn[[2]]))
        dn[[2]]
    else {
        if (do.NULL)
            NULL
        else paste(prefix, seq(length = NCOL(x)), sep = "")
    }
}

So if x has colnames that's what you get, irrespective of
"prefix".

-- 
   O__  ---- Peter Dalgaard             ??ster Farimagsgade 5, Entr.B
  c/ /'_ --- Dept. of Biostatistics     PO Box 2099, 1014 Cph. K
 (*) \(*) -- University of Copenhagen   Denmark          Ph:  (+45) 35327918
~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk)                  FAX: (+45) 35327907

On Wed, 20 Jul 2005 jhainm at fas.harvard.edu wrote:
>
> Hi,
>
> I would like to add a prefix to colnames in a matrix but I can't get
the prefix
> option in colnames to work. What am I doing wrong?
>
>> X<-matrix(NA,3,4)
>>
colnames(X)<-c("test","test","test","test")
>> colnames(X)<-colnames(X,prefix="PREFIX.")
>> X
>     test test test test
> [1,]   NA   NA   NA   NA
> [2,]   NA   NA   NA   NA
> [3,]   NA   NA   NA   NA
>
> ?? I also tried with do.NULL set to FALSE but it still does not work.
The help page is your friend here:

  do.NULL: logical.  Should this create names if they are 'NULL'?

   prefix: for created names.

      If 'do.NULL' is 'FALSE', a character vector (of length
'NROW(x)'
      or 'NCOL(x)') is returned in any case, prepending 'prefix'
to
      simple numbers, if there are no dimnames or the corresponding
                      ^^^^^^^^^^^^^^^^^^^^^^^^
      component of the dimnames is 'NULL'.

so
> X < -matrix(NA,3,4)
> colnames(X,prefix="PREFIX.", do.NULL=FALSE)
[1] "PREFIX.1" "PREFIX.2" "PREFIX.3"
"PREFIX.4"

works as documented.


-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595