Just a quick update on this thread.
The version of expand.dft() that I posted earlier has a bug in it.
This is the result of the use of lapply() and the evaluation of the
additional arguments passed to type.convert().
I noted this when testing the function on the UCBAdmissions data set,
which is a multi-way table used in some help file examples such
as ?as.data.frame.table.
Here is a corrected version:
expand.dft <- function(x, na.strings = "NA", as.is = FALSE, dec = ".")
{
DF <- sapply(1:nrow(x), function(i) x[rep(i, each = x$Freq[i]), ],
simplify = FALSE)
DF <- subset(do.call("rbind", DF), select = -Freq)
for (i in 1:ncol(DF))
{
DF[[i]] <- type.convert(as.character(DF[[i]]),
na.strings = na.strings,
as.is = as.is, dec = dec)
}
DF
}
Thus if we now take the UCBAdmissions multi-way table data and convert
it to a flat contingency table:
FCT <- as.data.frame(UCBAdmissions)
> FCT
Admit Gender Dept Freq
1 Admitted Male A 512
2 Rejected Male A 313
3 Admitted Female A 89
4 Rejected Female A 19
5 Admitted Male B 353
6 Rejected Male B 207
7 Admitted Female B 17
8 Rejected Female B 8
9 Admitted Male C 120
10 Rejected Male C 205
11 Admitted Female C 202
12 Rejected Female C 391
13 Admitted Male D 138
14 Rejected Male D 279
15 Admitted Female D 131
16 Rejected Female D 244
17 Admitted Male E 53
18 Rejected Male E 138
19 Admitted Female E 94
20 Rejected Female E 299
21 Admitted Male F 22
22 Rejected Male F 351
23 Admitted Female F 24
24 Rejected Female F 317
Thus, there should be:
> sum(FCT$Freq)
[1] 4526
rows in the final 'raw' data frame.
> DF <- expand.dft(FCT)
> str(DF)
'data.frame': 4526 obs. of 3 variables:
$ Admit : Factor w/ 2 levels "Admitted","Rejected": 1 1 1 1 1 1 1 1 1
1 ...
$ Gender: Factor w/ 2 levels "Female","Male": 2 2 2 2 2 2 2 2 2 2 ...
$ Dept : Factor w/ 6 levels "A","B","C","D",..: 1 1 1 1 1 1 1 1 1
1 ...
Note that the three columns are coerced back to factors, which is of
course the default behavior for data frames.
If we now use:
> DF <- expand.dft(FCT, as.is = TRUE)
> str(DF)
'data.frame': 4526 obs. of 3 variables:
$ Admit : chr "Admitted" "Admitted" "Admitted" "Admitted" ...
$ Gender: chr "Male" "Male" "Male" "Male" ...
$ Dept : chr "A" "A" "A" "A" ...
The three columns stay as character vectors. It was this behavior that
did not work properly in the first version.
HTH,
Marc Schwartz
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