[R] How to avoid automatic coercion to factor?

[Prof Brian Ripley]

Deepayan is correct, but note that I() creates a column of class "AsIs", 
not "character".  We should ask why you want character columns in a data 
frame?   (Certainly prior to 1.8.0 there is a fair chance that unless they 
are of class "AsIs" manipulations would turn them into factors.)

If you really want character columns, the way to do it is underhand:

f <- function() {
    a <- list(Int1=1:5,Char1=letters[1:5],Char2=letters[6:10])
    attr(a, "row.names") <- 1:5
    attr(a, "class") <- "data.frame"
    a
}

However, you might consider returning a list.


On Tue, 2 Sep 2003, Deepayan Sarkar wrote:

> 
> >From ?data.frame:
> 
>      Character variables passed to 'data.frame' are converted
>      to factor columns unless protected by 'I'. If a list or data frame
>      or matrix is passed to 'data.frame' it is as if each column had
>      been passed as a separate argument.
> 
> See the Examples section for an example.
> 
> On Tuesday 02 September 2003 17:30, Dutky, Steve wrote:
> > I have a function that manipulates a list of numeric and character
> > components of equal length and wants to return a data.frame.
> >
> > EG,
> >
> > f<-function() {
> > 	a<-list(Int1=1:5,Char1=letters[1:5],Char2=letters[6:10])
> > 	b<-data.frame(a)
> > }
> >
> > How can I get the columns Char1, Char2, (...CharN) returned coerced to
> > character and not factor?
> >
> > It appears that I could coerce individual columns by
> > b$CharI<-as.character(b$CharI). Is there a less ugly way of doing this?
> 
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> 

-- 
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)
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