[R] Prefix for colnames

[Prof Brian Ripley]

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)
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