I found an answer in "?unclass" and a minor difference between R 1.7.1 and S-Plus 6.1.2:

First ?unclass in R 1.7.1 under Windows 2000:

     Many R objects have a `class' attribute, a character vector giving
     the names of the classes which the object ``inherits'' from. If
     the object does not have a class attribute, it has an implicit
     class, `"matrix"', `"array"' or the result of `mode(x)'.
...
     The function `class' prints the vector of names of classes an
     object inherits from.
...
     `unclass' returns (a copy of) its argument with its class
     attribute removed.

Thus, "incidencia <- unclass(incidencia)" removed the class attribute from "incidencia". Then consistent with the documentation, "class(incidencia)" has an implicit class "array"; if it were not a matrix or array, then "class(incidencia)" would have returned the result of mode(x).

Now, a trivial comparison between R 1.7.1 and S-Plus 6.1.2:

##R 1.7.1
> tst <- 2
> class(tst)
[1] "numeric"
> Tst <- unclass(tst)
> class(Tst)
[1] "numeric"
> mode(Tst)
[1] "numeric"

## Same thing in S-Plus 6.1.2:
> tst <- 2
> class(tst)
[1] "integer"
> Tst <- unclass(tst)
> class(Tst)
[1] "integer"
> mode(Tst)
[1] "numeric"

Note that "tst" and "Tst" have class and mode "numeric" in R 1.7.1 but class "integer" and mode "numeric" in S-Plus 6.1.2.

hope this helps. spencer graves

kjetil brinchmann halvorsen wrote:
Have I been sleeping in class?

rw1071 from CRAN, windows XP

incidencia is made by a call to tapply


class(incidencia)

[1] "array"


incidencia <- unclass(incidencia)
class(incidencia)

[1] "array"



Kjetil Halvorsen


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