Following some discussion on R-help, I'd like to propose that an
as.matrix method be added
to those available for ftable objects. The reason for this is that
there are a variety of situations
where one needs to flatten a 3+ way table, but then use that for
analysis as a matrix, not just for
pretty-printing. There is an as.table method to turn the result back to
a table, but an as.matrix
method is missing.
> methods(class="ftable")
[1] as.data.frame.ftable* as.table.ftable* format.ftable*
[4] head.ftable* print.ftable tail.ftable*
Non-visible functions are asterisked
>
The function below was proposed by William Dunlop:
# as.matrix method for flattened tables
# modified from Willaim Dunlop, <wdunlap at tibco.com>, R-Help, 01-09-2014
as.matrix.ftable <- function(x, sep="_", ...) {
makeDimNames <- function(vars) {
structure(
list(do.call(paste, c(rev(expand.grid(rev(vars))),
list(sep=sep)))),
names = paste(collapse=sep, names(vars))
)
}
structure(
unclass(x),
dimnames=c(makeDimNames(attr(x, "row.vars")),
makeDimNames(attr(x, "col.vars"))),
row.vars=NULL,
col.vars=NULL)
}
Some test cases:
> UCB <- UCBAdmissions
> as.matrix(ftable(Dept ~ Admit + Gender, data=UCB))
Dept
Admit_Gender A B C D E F
Admitted_Male 512 353 120 138 53 22
Admitted_Female 89 17 202 131 94 24
Rejected_Male 313 207 205 279 138 351
Rejected_Female 19 8 391 244 299 317
> as.matrix(ftable(Dept ~ ., data=UCB))
Dept
Admit_Gender A B C D E F
Admitted_Male 512 353 120 138 53 22
Admitted_Female 89 17 202 131 94 24
Rejected_Male 313 207 205 279 138 351
Rejected_Female 19 8 391 244 299 317
> as.matrix(ftable(Admit + Gender ~ Dept, data=UCB))
Admit_Gender
Dept Admitted_Male Admitted_Female Rejected_Male Rejected_Female
A 512 89 313 19
B 353 17 207 8
C 120 202 205 391
D 138 131 279 244
E 53 94 138 299
F 22 24 351 317
> as.matrix(ftable(Admit ~ ., data=UCB))
Admit
Gender_Dept Admitted Rejected
Male_A 512 313
Male_B 353 207
Male_C 120 205
Male_D 138 279
Male_E 53 138
Male_F 22 351
Female_A 89 19
Female_B 17 8
Female_C 202 391
Female_D 131 244
Female_E 94 299
Female_F 24 317
>
Related functions: The vcd package defines a more extensive suite of
similar structable functions,
including as.matrix.structable; however that function doesn't supply
appropriate dimnames for
the dimensions. Given as.matrix.ftable(), that is easy to correct:
# use as.matrix.ftable, but
# need to remove other attributes: dnames, split_vertical
library(vcd)
as.matrix.structable <- function(x, sep="_", ...) {
structure(
as.matrix.ftable(x, sep, ...),
dnames = NULL,
split_vertical = NULL
)
}
Test:
> as.matrix(structable(Gender ~ Admit + Dept, data=UCB))
Gender
Admit_Dept Male Female
Admitted_A 512 89
Admitted_B 353 17
Admitted_C 120 202
Admitted_D 138 131
Admitted_E 53 94
Admitted_F 22 24
Rejected_A 313 19
Rejected_B 207 8
Rejected_C 205 391
Rejected_D 279 244
Rejected_E 138 299
Rejected_F 351 317
> as.matrix(structable(Gender + Admit ~ Dept, data=UCB))
Gender_Admit
Dept Male_Admitted Male_Rejected Female_Admitted Female_Rejected
A 512 313 89 19
B 353 207 17 8
C 120 205 202 391
D 138 279 131 244
E 53 138 94 299
F 22 351 24 317
>
--
Michael Friendly Email: friendly AT yorku DOT ca
Professor, Psychology Dept. & Chair, Quantitative Methods
York University Voice: 416 736-2100 x66249 Fax: 416 736-5814
4700 Keele Street Web: http://www.datavis.ca
Toronto, ONT M3J 1P3 CANADA
