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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