[R] xtabs ignores l.h.s. rows with NA in just one column - bug or facility?

[David L Carlson]

The documentation describes how to control the behavior of missing values:

> xtabs( cbind(xx,yy) ~ ff, addNA=TRUE) 
   
ff  xx yy
  a 17   
  b 55 66

But of course, now you do not get 26 in the (a, yy) cell because 26 + NA = NA.

----------------------------------------
David L Carlson
Department of Anthropology
Texas A&M University
College Station, TX 77843-4352

-----Original Message-----
From: R-help <r-help-bounces using r-project.org> On Behalf Of Bendix Carstensen
Sent: Thursday, April 25, 2019 6:59 AM
To: r-help using r-project.org
Subject: [R] xtabs ignores l.h.s. rows with NA in just one column - bug or facility?

Here is an example showing that xtabs and cbind are not commutative, which at least I thought reading the help page for xtabs.

print( sessionInfo(), l=F )
xx <- c( 6,11,38,17)
yy <- c(NA,26,18,48)
ff <- c('a','a','b','b')
data.frame( xx, yy, ff )
xtabs( cbind(xx,yy) ~ ff )
cbind( xtabs(xx ~ ff ),
       xtabs(yy ~ ff ) )

Here is the result from my xomputer:

> print( sessionInfo(), l=F )
R version 3.5.3 (2019-03-11)
Platform: x86_64-pc-linux-gnu (64-bit)
Running under: Ubuntu 14.04.6 LTS

Matrix products: default
BLAS: /usr/lib/openblas-base/libopenblas.so.0
LAPACK: /usr/lib/lapack/liblapack.so.3.0

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

loaded via a namespace (and not attached):
[1] compiler_3.5.3
> xx <- c( 6,11,38,17)
> yy <- c(NA,26,18,48)
> ff <- c('a','a','b','b')
> data.frame( xx, yy, ff )
  xx yy ff
1  6 NA  a
2 11 26  a
3 38 18  b
4 17 48  b
> xtabs( cbind(xx,yy) ~ ff )

ff  xx yy
  a 11 26
  b 55 66
> cbind( xtabs(xx ~ ff ),
+        xtabs(yy ~ ff ) )
  [,1] [,2]
a   17   26
b   55   66
>

I would have guessed the upper left entry would be 17 in the first instance too, but it appears that xtabs does something like complete.cases() on the l.h.s. before summing. At least this should be in the description.

Am I missing something here?
Bendix Carstensen
Steno Diabetes Center Copenhagen

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