[Rd] xtabs and NA

[Milan Bouchet-Valat]

Le lundi 09 février 2015 à 14:52 +0100, Kirill Müller a écrit :
> 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.
The best workaround (but still using xtabs()) I have found up to now is
to surround variables with addNA(). But I agree this situation is very
painful, especially since the docs do not say anything about how to get
the NAs to appear.


Regards

> 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
> 
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