R devel - Sep 2000 - "[.data.frame" forgets about "AsIs" (PR#665)

Short example:

 > str(d <- data.frame(a = I(letters[1:5])))
 `data.frame':	5 obs. of  1 variable:
  $ a:Class 'AsIs'  chr [1:5] "a" "b" "c"
"d" ...
 > str(d[TRUE,,drop = FALSE])
 `data.frame':	5 obs. of  1 variable:
  $ a: chr  "a" "b" "c" "d" ...

The real problem about this is, that as soon as the data.frame is further
"transformed", the character component is coerced to a factor, e.g.

   > str(rbind(d[TRUE,,drop = FALSE], "E"))
   `data.frame':	6 obs. of  1 variable:
    $ a: Factor w/ 6 levels
"a","b","c","d",..: 1 2 3 4 6 5

--- 

I'm looking at a fix myself.

Martin Maechler <maechler@stat.math.ethz.ch>
http://stat.ethz.ch/~maechler/
Seminar fuer Statistik, ETH-Zentrum  LEO D10	Leonhardstr. 27
ETH (Federal Inst. Technology)	8092 Zurich	SWITZERLAND
phone: x-41-1-632-3408		fax: ...-1228			<><

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>>>>> "MM" == Martin Maechler
<maechler@stat.math.ethz.ch> writes:
    MM> Short example:
    >> str(d <- data.frame(a = I(letters[1:5])))
    MM> `data.frame':	5 obs. of  1 variable:
    MM> $ a:Class 'AsIs'  chr [1:5] "a" "b"
"c" "d" ...
    >> str(d[TRUE,,drop = FALSE])
    MM> `data.frame':	5 obs. of  1 variable:
    MM> $ a: chr  "a" "b" "c" "d" ...

    MM> The real problem about this is, that as soon as the data.frame is
    MM> further "transformed", the character component is coerced
to a
    MM> factor, e.g.

    >> str(rbind(d[TRUE,,drop = FALSE], "E"))
    MM> `data.frame':	6 obs. of  1 variable:
    MM> $ a: Factor w/ 6 levels
"a","b","c","d",..: 1 2 3 4 6 5


Probably the cleanest fix is the addition of 

  "[.AsIs" <- function(x, i) structure(NextMethod("["),
class = class(x))

--
Will go into R-devel unless someone has a better idea.

Martin Maechler <maechler@stat.math.ethz.ch>
http://stat.ethz.ch/~maechler/
Seminar fuer Statistik, ETH-Zentrum  LEO D10	Leonhardstr. 27
ETH (Federal Inst. Technology)	8092 Zurich	SWITZERLAND
phone: x-41-1-632-3408		fax: ...-1228			<><

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r-devel mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html
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