[Rd] xtabs and NA

[Kirill Müller]

Hi


I haven't found a way to produce a tabulation from factor data with NA 
values using xtabs. Please find a minimal example below, it's also on 
R-pubs [1]. Tested with R 3.1.2 and R-devel r67720.

It doesn't seem to be documented explicitly that it's not supported. 
 From reading the code [2] it looks like the relevant call to table() 
doesn't set the "useNA" parameter, which I think is necessary to make 
NAs show up in the result.

Am I missing anything? If this a bug -- would a patch be welcome? Do we 
need compatibility with the current behavior?

I'm aware of workarounds, I just prefer xtabs() over table() for its 
interface.

Thanks.


Best regards

Kirill


[1] http://rpubs.com/krlmlr/xtabs-NA
[2] 
https://github.com/wch/r-source/blob/780021752eb83a71e2198019acf069ba8741103b/src/library/stats/R/xtabs.R#L60


data <- factor(letters[1:4], levels = letters[1:3])
data
## [1] a    b    c    <NA>
## Levels: a b c
xtabs(~data)
## data
## a b c
## 1 1 1
xtabs(~data, na.action = na.pass)
## data
## a b c
## 1 1 1
xtabs(~data, na.action = na.pass, exclude = numeric())
## data
## a b c
## 1 1 1
xtabs(~data, na.action = na.pass, exclude = NULL)
## data
## a b c
## 1 1 1
sessionInfo()
## R version 3.1.2 (2014-10-31)
## Platform: x86_64-pc-linux-gnu (64-bit)
##
## locale:
##  [1] LC_CTYPE=en_US.UTF-8       LC_NUMERIC=C
##  [3] LC_TIME=de_CH.UTF-8        LC_COLLATE=en_US.UTF-8
##  [5] LC_MONETARY=de_CH.UTF-8    LC_MESSAGES=en_US.UTF-8
##  [7] LC_PAPER=de_CH.UTF-8       LC_NAME=C
##  [9] LC_ADDRESS=C               LC_TELEPHONE=C
## [11] LC_MEASUREMENT=de_CH.UTF-8 LC_IDENTIFICATION=C
##
## attached base packages:
## [1] stats     graphics  grDevices utils     datasets  methods base
##
## other attached packages:
## [1] magrittr_1.5            ProjectTemplate_0.6-1.0
##
## loaded via a namespace (and not attached):
## [1] digest_0.6.8    evaluate_0.5.7  formatR_1.0.3 htmltools_0.2.6
## [5] knitr_1.9.2     rmarkdown_0.5.1 stringr_0.6.2 tools_3.1.2
## [9] ulimit_0.0-2