I have an application where I have a function to calculate results for
a 2-way table or matrix, which
returns a matrix with one less row and column. To keep this short, the
function below captures the structure:
fun2way <- function(f){
if (!length(dim(f)) ==2) stop("only for 2-way arrays")
R <- dim(f)[1]
C <- dim(f)[2]
f[1:(R-1), 1:(C-1)]
}
Now, I want to extend this to higher-way arrays, using apply-like
methods over the strata (all but the first two dimensions),
and returning an array in which the last dimensions correspond to
strata. That is, I want to define something like the
following using an a*ply method, but aaply gives a result in which the
applied .margin(s) do not appear last in the
result, contrary to the documentation for ?aaply. I think this is a
bug, either in the function or the documentation,
but perhaps there's something I misunderstand for this case.
fun <- function(f, stratum=NULL) {
L <- length(dim(f))
if (L > 2 && is.null(stratum))
stratum <- 3:L
if (is.null(stratum)) {
result <- fun2way(f)
}
else {
require(plyr)
result <- aaply(f, stratum, fun2way) ## order of dimensions
screwed up!
}
result
}
For example, by hand (or with a loop) I can calculate the
pieces and combine them as I want using abind():
> # apply separately to strata
> t1<-fun2way(HairEyeColor[,,1])
> t2<-fun2way(HairEyeColor[,,2])
>
> library(abind)
> abind(t1, t2, along=3)
, , 1
Brown Blue Hazel
Black 32 11 10
Brown 53 50 25
Red 10 10 7
, , 2
Brown Blue Hazel
Black 36 9 5
Brown 66 34 29
Red 16 7 7
alply() gives me what I want, but with the strata as list elements,
rather than an array
> library(plyr)
> # strata define separate list elements
> alply(HairEyeColor, 3, fun2way)
$`1`
Eye
Hair Brown Blue Hazel
Black 32 11 10
Brown 53 50 25
Red 10 10 7
$`2`
Eye
Hair Brown Blue Hazel
Black 36 9 5
Brown 66 34 29
Red 16 7 7
attr(,"split_type")
[1] "array"
attr(,"split_labels")
Sex
1 Male
2 Female
>
However, with aaply(), dim[3] ends up as first dimension, not last
> # dim[3] ends up as first dimension, not last
> aaply(HairEyeColor, 3, fun2way)
, , Eye = Brown
Hair
Sex Black Brown Red
Female 36 66 16
Male 32 53 10
, , Eye = Blue
Hair
Sex Black Brown Red
Female 9 34 7
Male 11 50 10
, , Eye = Hazel
Hair
Sex Black Brown Red
Female 5 29 7
Male 10 25 7
> str(aaply(as.array(HairEyeColor), 3, fun2way))
num [1:2, 1:3, 1:3] 36 32 66 53 16 10 9 11 34 50 ...
- attr(*, "dimnames")=List of 3
..$ Sex : chr [1:2] "Female" "Male"
..$ Hair: chr [1:3] "Black" "Brown" "Red"
..$ Eye : chr [1:3] "Brown" "Blue" "Hazel"
>
> ## aaply should return this....
> aperm(aaply(HairEyeColor, 3, fun2way), c(2,3,1))
, , Sex = Female
Eye
Hair Brown Blue Hazel
Black 36 9 5
Brown 66 34 29
Red 16 7 7
, , Sex = Male
Eye
Hair Brown Blue Hazel
Black 32 11 10
Brown 53 50 25
Red 10 10 7
>
On the other hand, aaply() does work as I expect, with an array of size
2 x C x strata
> library(vcd)
> fun2way(Employment[,,1])
<1Mo 1-3Mo 3-12Mo 1-2Yr 2-5Yr
8 35 70 62 56
> fun2way(Employment[,,2])
<1Mo 1-3Mo 3-12Mo 1-2Yr 2-5Yr
40 85 181 85 118
>
> aaply(Employment, 3, fun2way)
LayoffCause <1Mo 1-3Mo 3-12Mo 1-2Yr 2-5Yr
Closure 8 35 70 62 56
Replaced 40 85 181 85 118
--
Michael Friendly Email: friendly AT yorku DOT ca
Professor, Psychology Dept.
York University Voice: 416 736-5115 x66249 Fax: 416 736-5814
4700 Keele Street Web: http://www.datavis.ca
Toronto, ONT M3J 1P3 CANADA
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