R help - Jul 2011 - Access only part of last dimension of table/matrix

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.


David Winsemius, MD
West Hartford, CT

On Jul 1, 2011, at 5:50 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:
Sorry, I had meant to poste a test dataset:

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) )
>
> 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?
>
I did come up with a solution:

apply(etbl2, 1:(length(dim(Etbl2))-1), "[", 2)

Doesn't seem as elegant as I might have liked but it "works". And
I
had puzzled and searched in the archives, SO, and multiple books  
without finding a worked example.

> Thnks.
>
> -- 
> David.
>
>
> David Winsemius, MD
> West Hartford, CT
>
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> and provide commented, minimal, self-contained, reproducible code.
David Winsemius, MD
West Hartford, CT

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.

Hope that this helps.

Regards,

Marc Schwartz

On 07/02/2011 07:50 AM, 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?
>
Hi David,
I used to do something like this before completely reprogramming the 
barNest function.

# set the first dimension (can be the last also) to a number "stat"
sliceargs[[1]] <- x[[stat]]
# for the rest of the dimensions of this array, tack on a comma
for (arg in 2:ndim) sliceargs[[arg]] <- TRUE
  sliceargs[[ndim + 1]] <- slice
# "slice" the array
xslice[[stat]] <- do.call("[", sliceargs)

To get the last dimension, just tack commas together for 1:(ndim-1) and 
then add the number at the end.
I think Bill Dunlap gave me this solution when I was struggling with it.

Jim

On Jul 2, 2011, at 5:39 AM, peter dalgaard wrote:
> 
> On Jul 2, 2011, at 03:29 , Marc Schwartz wrote:
> 
>> It actually scared me that I had any recollection of an isolated post
from 10 years ago. Not sure what to make of that...
> 
> If it is any consolation, the author had forgotten it entirely....
LOL Peter! Thanks!

Regards,

Marc