R devel - Apr 2013 - Subset of a 'table' divided by a 'table' is a 'table', but printed by 'print.default'

This is just info.

I recently got something like this.
> x <- factor(c("A","A","B","B"),
levels=c("A","B"))
> y <- factor(c("a","b","a","b"),
levels=c("a","b"))
> table(x, y)[, "a"] / table(x)
x
  A   B
0.5 0.5
attr(,"class")
[1] "table"

The printing indicates that the result is of class 'table'. But, the
'print' method of class 'table' does not print
attr(,"class"). It seems that 'print.default' is used in the
printing. I am OK with it, just unusual.

I think, that is another symptom of an already known behavior as in the
following:
- PR#2345: difftime arithmetic
- PR#13209: S4 object does not commute?

> sessionInfo()
R version 3.0.0 (2013-04-03)
Platform: i386-w64-mingw32/i386 (32-bit)

locale:
[1] LC_COLLATE=English_United States.1252
[2] LC_CTYPE=English_United States.1252
[3] LC_MONETARY=English_United States.1252
[4] LC_NUMERIC=C
[5] LC_TIME=English_United States.1252

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base

On 13-04-30 3:38 AM, Suharto Anggono Suharto Anggono
wrote:
> This is just info.
>
> I recently got something like this.
>
>> x <-
factor(c("A","A","B","B"),
levels=c("A","B"))
>> y <-
factor(c("a","b","a","b"),
levels=c("a","b"))
>> table(x, y)[, "a"] / table(x)
> x
>    A   B
> 0.5 0.5
> attr(,"class")
> [1] "table"
>
> The printing indicates that the result is of class 'table'. But,
the 'print' method of class 'table' does not print
attr(,"class"). It seems that 'print.default' is used in the
printing. I am OK with it, just unusual.
>
> I think, that is another symptom of an already known behavior as in the
following:
> - PR#2345: difftime arithmetic
> - PR#13209: S4 object does not commute?
There are no S4 objects or time objects involved here, so it's likely 
something different.

I notice the following strange behaviour.  If I save the ratio in a 
variable, it prints differently with an explicit print than with auto 
printing:

x <- factor(c("A","A","B","B"),
levels=c("A","B"))
y <- factor(c("a","b","a","b"),
levels=c("a","b"))
ratio <- table(x, y)[, "a"] / table(x)
ratio          # shows what you saw
print(ratio)   # shows what you expected


Something else that's a little strange:  the numerator does not have 
class "table", so you can get the same results with

ratio <- c(1,1) / table(x)

Looking at the internals, I see that the ratio variable has a class 
attribute, but does not have its "object bit" set.

So it looks like the bug is in the implementation of "/".  Either it 
should drop the class, or it should set the object bit.

The difference in printing between auto-printing and explicit printing 
may be worth addressing, but really objects like ratio shouldn't exist, 
so it's not surprising that they behave strangely.

Duncan Murdoch

>
>
>> sessionInfo()
> R version 3.0.0 (2013-04-03)
> Platform: i386-w64-mingw32/i386 (32-bit)
>
> locale:
> [1] LC_COLLATE=English_United States.1252
> [2] LC_CTYPE=English_United States.1252
> [3] LC_MONETARY=English_United States.1252
> [4] LC_NUMERIC=C
> [5] LC_TIME=English_United States.1252
>
> attached base packages:
> [1] stats     graphics  grDevices utils     datasets  methods   base
>
> ______________________________________________
> R-devel at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel
>

On Tue, Apr 30, 2013 at 10:49 AM, Duncan Murdoch
<murdoch.duncan at gmail.com> wrote:
> So it looks like the bug is in the implementation of "/".  Either
it
> should drop the class, or it should set the object bit.
>
> The difference in printing between auto-printing and explicit printing
> may be worth addressing, but really objects like ratio shouldn't exist,
> so it's not surprising that they behave strangely.
 Also happens with *, if LHS is not a scalar:

 > c(1,1)*table(x)
x
A B
2 2
attr(,"class")
[1] "table"

 > 1*table(x)
x
A B
2 2

 - similar with + and -, but not unary + and -.

 Nice to see a bug in arithmetic operators that isn't covered by
everyone screaming "FAQ 7.31!!!"

Barry

On 13-04-30 3:38 AM, Suharto Anggono Suharto Anggono
wrote:
> This is just info.
>
> I recently got something like this.
>
>> x <-
factor(c("A","A","B","B"),
levels=c("A","B"))
>> y <-
factor(c("a","b","a","b"),
levels=c("a","b"))
>> table(x, y)[, "a"] / table(x)
> x
>    A   B
> 0.5 0.5
> attr(,"class")
> [1] "table"
>
> The printing indicates that the result is of class 'table'. But,
the 'print' method of class 'table' does not print
attr(,"class"). It seems that 'print.default' is used in the
printing. I am OK with it, just unusual.
This is fixed as of r62697 in R-devel and R-patched.

The documentation in ?Arithmetic was also inaccurate, and has been 
modified.  The correct description is now:

   The rules for determining the attributes of the result are rather
   complicated.  Most attributes are taken from the longer argument.
   Names will be copied from the first if it is the same length as the
   answer, otherwise from the second if that is.  If the arguments are
   the same length, attributes will be copied from both, with those of
   the first argument taking precedence when the same attribute is
   present in both arguments. For time series, these operations are
   allowed only if the series are compatible, when the class and
   \code{\link{tsp}} attribute of whichever is a time series (the same,
   if both are) are used.  For arrays (and an array result) the
   dimensions and dimnames are taken from first argument if it is an
   array, otherwise the second.

This was true for R 3.0.0 and earlier as well, but before my patch while 
the class was copied from the second argument, the object bit was copied 
from the first argument.  Now things are consistent.

Duncan Murdoch

> I think, that is another symptom of an already known behavior as in the
following:
> - PR#2345: difftime arithmetic
> - PR#13209: S4 object does not commute?
>
>
>> sessionInfo()
> R version 3.0.0 (2013-04-03)
> Platform: i386-w64-mingw32/i386 (32-bit)
>
> locale:
> [1] LC_COLLATE=English_United States.1252
> [2] LC_CTYPE=English_United States.1252
> [3] LC_MONETARY=English_United States.1252
> [4] LC_NUMERIC=C
> [5] LC_TIME=English_United States.1252
>
> attached base packages:
> [1] stats     graphics  grDevices utils     datasets  methods   base
>
> ______________________________________________
> R-devel at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel
>