R devel - Dec 2012 - Suggestion of change to reduce overhead of 'table'

In R 2.7.2, if argument 'exclude' is not specified and input is already
a factor, function 'table' uses the input as is. In R 2.15.2, in the
same case, function 'table' always applies function 'factor' to
the input. The time spent by 'factor' is not long, but is not
negligible.


I suggest to change 'table' so that 'factor' is not called for
input that is already a factor when it is known that the resulting levels is as
in the input. This is diff against
https://svn.r-project.org/R/trunk/src/library/base/R/table.R.

85c85,88
<? ? ? ? ? ? ? ? ? ? ? ???a <- factor(a, levels = ll[!(ll %in% exclude)],
---
>? ? ? ? ? ? ? ? ? ? ? ???llexcl <- ll %in% exclude
>? ? ? ? ? ? ? ? ? ? ? ???if (any(llexcl) ||
>? ? ? ? ? ? ? ? ? ? ? ???(useNA == "no" &&
any(is.na(ll))))
>? ? ? ? ? ? ? ? ? ? ? ? ? ???factor(a, levels = ll[!llexcl],
86a90,91
>? ? ? ? ? ? ? ? ? ? ? ???else
>? ? ? ? ? ? ? ? ? ? ? ? ? ???a

Function 'table' calls function 'addNA' in some cases. I suggest
to change 'addNA', too. This is diff against
https://svn.r-project.org/R/trunk/src/library/base/R/factor.R.

336d335
<? ???if (ifany & !any(is.na(x))) return(x)
338c337,339
<? ???if (!any(is.na(ll))) ll <- c(ll, NA)
---
>? ???hasNAlev <- any(is.na(ll))
>? ???if ((ifany || hasNAlev) && !any(is.na(x))) return(x)
>? ???if (!hasNAlev) ll <- c(ll, NA)

Instead of calling 'factor', 'addNA' can also change
"levels" attribute and accordingly fill missing value in internal code
of the factor.