On Jul 1, 2011, at 8:15 PM, David Winsemius wrote:
>
> On Jul 1, 2011, at 7:44 PM, Marc Schwartz wrote:
>
>> On Jul 1, 2011, at 4:50 PM, David Winsemius wrote:
>>
>>>
>>> I would like to do some operations inside a function using only one value
>>> for the last dimension of a table/matrix:
>>>
>>> tabfn <- function (dfrm, facvec, YN ="event"){
>>> return( Etbl <- do.call(table, dfrm[ , c(facvec, "event") ]) )
>>> # just want Etbl[,,,"TRUE"] or Etbl[,, "TRUE"] or Etbl[,"TRUE"]
>>> }
>>> tbl <- tabfn(testdf, c("x", "y") )
>>> tbl # all value of event returned
>>>
>>> At the console it is easy for me to count the number of factors and use the
>>> right number of commas
>>>
>>> tbl[ , , "TRUE"] if I only want the slice with that value. How can I do
>>> this programmatically?
>>>
>>> Thnks.
>>
>>
>> David,
>>
>> I had a vague recollection of something like this coming up at some point in
>> the past and it took me a bit to get the right keywords to find it.
>>
>> I did not realize how far back it was (2001), but here are two possible
>> solutions by Peter Dalgaard and Thomas Lumley from the same thread:
>>
>> https://stat.ethz.ch/pipermail/r-help/2001-October/016110.html
>> https://stat.ethz.ch/pipermail/r-help/2001-October/016122.html
>>
>> It looks like Peter's solution is along the lines of the one that you just
>> posted.
>
>
> Yeah. Thanks, Mark. Pretty much the same. Guess I'm in good company.
> (Surprised this isn't asked more frequently.)
>
> testdf <- data.frame(x=sample(letters[1:5], 25, replace=TRUE),
> y=sample(letters[1:5], 25, replace=TRUE),
> z=sample(letters[1:5], 25, replace=TRUE),
> event=sample(c(TRUE, FALSE), 25, replace=TRUE) )
>
> etbl <- table(testdf[ , c(c("x", "y"), "event")])
> apply(etbl, seq(length=length(dim(etbl))-1),"[", 2) # Dalgaard 2001
> apply(etbl, 1:(length(dim(etbl))-1), "[", 2) # Winsemius 2011
>
> Any idea how to make it a "selection"? By that I mean how to select values of
> the last dimension whose "event" values are "TRUE". I get "Error: object
> 'event' not found" with any expression involving event, since it is only an
> attribute in dimnames.
>
>
>>
>> Hope that this helps.
>
> Yes. At least there is nothing (yet) that I would call "truly elegant". Maybe
> it's just that I stumbled on my solution, rather than seeing it as a
> glaringly obvious application of apply(..., "[" , index)
>
>>
>> Regards,
>
> Sorry for the duplicate private message. Meant to hit reply to all.
Not a problem David, I was just in the process of replying to it when I saw
this reply.
Try this:
> apply(etbl, seq(length=length(dim(etbl))-1), function(x) x["TRUE"])
y
x a b c d e
a 0 1 1 0 0
b 1 0 0 1 0
c 0 0 0 0 0
d 1 0 0 0 2
e 0 1 0 1 0
Seems to work here, at least on your example data, but not fully tested on
higher dimensional arrays.
I also tried it on the UCBAdmissions data set:
> str(UCBAdmissions)
table [1:2, 1:2, 1:6] 512 313 89 19 353 207 17 8 120 205 ...
- attr(*, "dimnames")=List of 3
..$ Admit : chr [1:2] "Admitted" "Rejected"
..$ Gender: chr [1:2] "Male" "Female"
..$ Dept : chr [1:6] "A" "B" "C" "D" ...
Get Dept == "C":
> apply(UCBAdmissions, seq(length=length(dim(UCBAdmissions))-1), function(x)
> x["C"])
Gender
Admit Male Female
Admitted 120 202
Rejected 205 391
It actually scared me that I had any recollection of an isolated post from 10
years ago. Not sure what to make of that...
Regards,
Marc
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