[R] Simple permutation question

[Jeff Newmiller]

sorry... editing on the fly... try:

perm.fixed <- function( x ) {
   if ( length( x ) == 1 ) return( matrix( x, nrow=1 ) )
   lst <- lapply( seq_along( x )
                , function( i ) {
                    cbind( x[ i ], perm.fixed( x[ -i ] ) )
                  }
                )
   do.call( rbind, lst )
}

On Wed, 25 Jun 2014, Jeff Newmiller wrote:

> The brokenness of your perm.broken function arises from the attempted use of 
> sapply to bind matrices together, which is not something sapply does.
>
> perm.fixed <- function( x ) {
>  if ( length( x ) == 1 ) return( matrix( x, nrow=1 ) )
>  lst <- lapply( seq_along( x )
>               , function( i ) {
>                   cbind( x[ i ], perm.jdn( x[ -i ] ) )
>                 }
>               )
>  do.call(rbind, lst)
> }
>
>
> On Wed, 25 Jun 2014, Robert Latest wrote:
>
>> So my company has hired a few young McKinsey guys from overseas for a
>> couple of weeks to help us with a production line optimization. They
>> probably charge what I make in a year, but that's OK because I just
>> never have the time to really dive into one particular time, and I have
>> to hand it to the consultants that they came up with one or two really
>> clever ideas to model the production line. Of course it's up to me to
>> feed them the real data which they then churn through their Excel
>> models that they cook up during the nights in their hotel rooms, and
>> which I then implement back into my experimental system using live data.
>> 
>> Anyway, whenever they need something or come up with something I skip
>> out of the room, hack it into R, export the CSV and come back in about
>> half the time it takes Excel to even read in the data, let alone
>> process it. Of course that gor them curious, and I showed off a couple
>> of scripts that condense their abysmal Excel convolutions in a few
>> lean and mean lines of R code.
>> 
>> Anyway, I'm in my office with this really attractive, clever young
>> McKinsey girl (I'm in my mid-forties, married with kids and all, but I
>> still enjoyed impressing a woman with computer stuff, of all things!),
>> and one of her models involves a simple permutation of five letters --
>> "A" through "E".
>> 
>> And that's when I find out that R doesn't have a permutation function.
>> How is that possible? R has EVERYTHING, but not that? I'm
>> flabbergasted. Stumped. And now it's up to me to spend the evening at
>> home coding that model, and the only thing I really need is that
>> permutation.
>> 
>> So this is my first attempt:
>> 
>> perm.broken <- function(x) {
>>    if (length(x) == 1) return(x)
>>    sapply(1:length(x), function(i) {
>>        cbind(x[i], perm(x[-i]))
>>    })
>> }
>> 
>> But it doesn't work:
>>> perm.broken(c("A", "B", "C"))
>>     [,1] [,2] [,3]
>> [1,] "A"  "B"  "C"
>> [2,] "A"  "B"  "C"
>> [3,] "B"  "A"  "A"
>> [4,] "C"  "C"  "B"
>> [5,] "C"  "C"  "B"
>> [6,] "B"  "A"  "A"
>>> 
>> 
>> And I can't figure out for the life of me why. It should work because I
>> go through the elements of x in order, use that in the leftmost column,
>> and slap the permutation of the remaining elements to the right. What
>> strikes me as particularly odd is that there doesn't even seem to be a
>> systematic sequence of letters in any of the columns. OK, since I
>> really need that function I wrote this piece of crap:
>> 
>> perm.stupid <- function(x) {
>>    b <- as.matrix(expand.grid(rep(list(x), length(x))))
>>    b[!sapply(1:nrow(b), function(r) any(duplicated(b[r,]))),]
>> }
>> 
>> It works, but words cannot describe its ugliness. And it gets really
>> slow really fast with growing x.
>> 
>> So, anyway. My two questions are:
>> 1. Does R really, really, seriously lack a permutation function?
>> 2. OK, stop kidding me. So what's it called?
>> 3. Why doesn't my recursive function work, and what would a
>>   working version look like?
>> 
>> Thanks,
>> robert
>> 
>> ______________________________________________
>> R-help at r-project.org mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-help
>> PLEASE do read the posting guide 
>> http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>> 
>
> ---------------------------------------------------------------------------
> Jeff Newmiller                        The     .....       .....  Go Live...
> DCN:<jdnewmil at dcn.davis.ca.us>        Basics: ##.#.       ##.#.  Live Go...
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>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>

---------------------------------------------------------------------------
Jeff Newmiller                        The     .....       .....  Go Live...
DCN:<jdnewmil at dcn.davis.ca.us>        Basics: ##.#.       ##.#.  Live Go...
                                       Live:   OO#.. Dead: OO#..  Playing
Research Engineer (Solar/Batteries            O.O#.       #.O#.  with
/Software/Embedded Controllers)               .OO#.       .OO#.  rocks...1k