[R] data.frame

[Peter Dalgaard BSA]

Chong Gu <chong at stat.purdue.edu> writes:

> I am not sure if I should call this a bug or just a design
> imperfection.
> 
> I have noticed that the data.frame function does not preserve the
> integrity of multivariate components.  Here is a simple illustration:
> 
> > x <- matrix(1:6,3,2)
> > y <- 1:3
> > z <- data.frame(x=x,y=y)
> > z$x 
> # NULL
> > z$y 
> # [1] 1 2 3
> 
> One can however get by that by using model.frame:
> 
> > zz <- model.frame(~x+y)
> > zz$x
> #      [,1] [,2]
> # [1,]    1    4
> # [2,]    2    5
> # [3,]    3    6
> 
> I was expecting data.frame to behave like this.

You're not the first... This apparently goes back to a design decision
that data.frame be used to coerce matrices to data frames. You can get
the desired behaviour with the I() function:

> z <- data.frame(x=I(x),y=y)
> z$x
     [,1] [,2]
[1,]    1    4
[2,]    2    5
[3,]    3    6
attr(,"class")
[1] "AsIs"


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