Hello,
Currently it's possible to convert an object of class table to a data frame
with as.data.frame.table(), but there's no ready-made function, AFAIK, to do
the reverse operation, i.e. conversion of a data frame to a table.
Do you think it would be a good idea to add a data.frame method to
as.table(), to allow such conversions?
The idea is that if `x' is a table and `y <- as.data.frame(x)', then the
object returned by `as.table(y)' should be equal to `x'.
Below is a proof of concept
as.table.data.frame <- function(x, ..., response) {
if (missing(response))
resp <- ncol(x)
else {
resp <- match(response[1L], names(x))
if (is.na(resp))
stop('not found: ', response[1L])
}
x[-resp] <- lapply(x[-resp], as.factor)
if (any(do.call(table, x[-resp]) > 1L))
stop('repeated frequency value')
dn <- lapply(x[-resp], function(y) {
if (any(is.na(y))) c(levels(y), NA) else levels(y)
})
ind <- mapply(function(val, lev) match(val, lev), x[-resp], dn)
out <- array(dim=unlist(lapply(dn, length)), dimnames=dn)
out[ind] <- x[[resp]]
as.table(out)
}
and a simple usage example:
> (y <- table(foo=c('a','a',NA,'b','b'), useNA='always'))
foo
a b <NA>
2 2 1
> (yy <- as.data.frame(y))
foo Freq
1 a 2
2 b 2
3 <NA> 1
> as.table(yy)
foo
a b <NA>
2 2 1
>
Any thoughts?
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