Filling Lists or Arrays of variable dimensions

David.
> 
> William, thats interesting, but not really helping the main problem, which is: how to do 
> 
>> l[[ as.character(grid[1, ]) ]] <- 1
> 
> without having initialized the list in the loop before. 
> 
> Well, or how to initialize it without having to do the loop thing, because the loop stuff can only be done for a specific set of parameter vectors. But those change, and i don't want to have to write another loop construct every time for the new version.
> 
> I want to say: hey, i have these vectors here with these values (my parameters), could you build me that nested list structure (tree - whatever) from it? And the function will give me that structure whatever i give it without me needing to intervene in form of changing the code.
> 
> -------------- Clarification -----------------
> 
> First: i am not computing statistics over the parameters. I'm computing stuff from other data, and the computation is affected by the parameters. 
> 
> I am computing classifiers for different sets of parameters for those classifiers. So the result of doSomething() isn't a simple value. Its usually a list of 6 lists (doing cross validation), which in turn have the classifier object, some statistics of the classifier (e.g what was missclassified), and the subsets of data used in them.
> That doesn't really fit in a data.frame, hence the use of lists. I want the nested lists because it helps me find stuff in the object browser faster, and because all my other code is already geared towards it. If i had the time i might still go for a flat structure that everyone keeps telling me to use (got a few mails off the list),
> but i really haven't the time.
> 
> If theres no good way i'll just keep things as they are now.
> 
> 
> On 20.12.2012, at 18:37, William Dunlap wrote:
> 
>> Arranging data as a list of lists of lists of lists [...] of scalar values generally
>> will lead to slow and hard-to-read R code, mainly because R is designed to
>> work on long vectors of simple data.  If you were to start over, consider constructing
>> a data.frame with one column for each attribute.  Then tools like aggregate and
>> the plyr functions would be useful.
>> 
>> However, your immediate problem may be solved by creating your 'grid' object
>> as a data.frame of character, not factor, columns because as.character works differently
>> on lists of scalar factors and lists of scalar characters.  Usually as.<mode>(x), when
>> x is a list of length-1 items, gives the same result as as.<mode>(unlist(x)), but not when
>> x is a list of length-1 factors:
>> 
>>> height<-c("high", "low")
>>> width<-c("slim", "wide")
>>> gridF <- expand.grid(height, width, stringsAsFactors=FALSE)
>>> gridT <- expand.grid(height, width, stringsAsFactors=TRUE)
>>> as.character(gridF[1,])
>> [1] "high" "slim"
>>> as.character(gridT[1,])
>> [1] "1" "1"
>>> as.character(unlist(gridT[1,])) # another workaround
>> [1] "high" "slim"
>> 
>> Your example was not self-contained so I changed the call to doSomething() to paste(h,w,sep="/"):
>> 
>> height<-c("high", "low")
>> width<-c("slim", "wide")
>> 
>> l <- list()
>> for(h in height){
>>         l[[h]] <- list()
>>         for(w in width){
>>                 l[[h]][[w]] <- paste(h, w, sep="/") # doSomething()
>>         }
>> }
>> 
>> grid <- expand.grid(height, width, stringsAsFactors=FALSE)
>> as.character(grid[1,])
>> # [1] "high" "slim", not the [1] "1" "1" you get with stringsAsFactors=TRUE
>> l[[ as.character(grid[1, ]) ]]
>> # [1] "high/slim"
>> l[[ as.character(grid[1, ]) ]] <- 1
>> l[[ as.character(grid[1, ]) ]]
>> # [1] 1
>> 
>> Bill Dunlap
>> Spotfire, TIBCO Software
>> wdunlap tibco.com
>> 
>>> -----Original Message-----
>>> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] On Behalf
>>> Of Jessica Streicher
>>> Sent: Thursday, December 20, 2012 8:43 AM
>>> To: Chris Campbell
>>> Cc: R help
>>> Subject: Re: [R] Filling Lists or Arrays of variable dimensions
>>> 
>>> Aggregate is highly confusing (and i would have appreciated if you used my example
>>> instead, i don't get it to do anything sensible on my stuff).
>>> 
>>> And this seems not what i asked for anyway. This may be a named list but not named and
>>> structured as i want it at all.
>>> 
>>> happy Christmas too
>>> 
>>> On 20.12.2012, at 15:48, Chris Campbell wrote:
>>> 
>>>> Dear Jessica
>>>> 
>>>> Aggregate is a function that allows you to perform loops across multiple variables.
>>>> 
>>>> tempData <- data.frame(height = rnorm(20, 100, 10),
>>>>  width = rnorm(20, 50, 5),
>>>>  par1 = rnorm(20))
>>>> 
>>>> tempData$htfac <- cut(tempData$height, c(0, 100, 200))
>>>> tempData$wdfac <- cut(tempData$width, c(0, 50, 100))
>>>> 
>>>> doSomething <- function(x) { mean(x) }
>>>> 
>>>> out <- aggregate(tempData["par1"], tempData[c("htfac", "wdfac")], doSomething)
>>>> 
>>>> # out is a data frame; this is a named list.
>>>> # use as.list to remove the data.frame class
>>>> 
>>>>> as.list(out)
>>>> 
>>>> $htfac
>>>> [1] (0,100]   (100,200] (0,100]   (100,200]
>>>> Levels: (0,100] (100,200]
>>>> 
>>>> $wdfac
>>>> [1] (0,50]   (0,50]   (50,100] (50,100]
>>>> Levels: (0,50] (50,100]
>>>> 
>>>> $par1
>>>> [1] -1.0449563 -0.3782483 -0.9319105  0.8837459
>>>> 
>>>> 
>>> 
>>>> 
>>>> I believe you are seeing an error similar to this one:
>>>> 
>>>>> out[[1:3]] <- 1
>>>> Error in `[[<-`(`*tmp*`, i, value = value) :
>>>> recursive indexing failed at level 2
>>>> 
>>>> This is because double square brackets for lists can only set a single list element at
>>> once; grid[1, ] is longer.
>>> 
>>>> 
>>>> Happy Christmas
>>>> 
>>>> Chris
>>>> 
>>>> 
>>>> Chris Campbell
>>>> Tel. +44 (0) 1249 705 450 | Mobile. +44 (0) 7929 628 349
>>>> mailto:ccampbell at mango-solutions.com | http://www.mango-solutions.com
>>>> Mango Solutions
>>>> 2 Methuen Park
>>>> Chippenham
>>>> Wiltshire
>>>> SN14 OGB
>>>> UK
>>>> 
>>>> -----Original Message-----
>>>> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] On Behalf
>>> Of Jessica Streicher
>>>> Sent: 20 December 2012 12:46
>>>> To: R help
>>>> Subject: [R] Filling Lists or Arrays of variable dimensions
>>>> 
>>>> Following problem:
>>>> 
>>>> Say you have a bunch of parameters and want to produce results for all combinations
>>> of those:
>>>> 
>>>> height<-c("high","low")
>>>> width<-c("slim","wide")
>>>> 
>>>> then what i used to do was something like this:
>>>> 
>>>> l<-list()
>>>> for(h in height){
>>>> 	l[[h]]<-list()
>>>> 	for(w in width){
>>>> 		l[[h]][[w]] <- doSomething()
>>>> 	}
>>>> }
>>>> 
>>>> Now those parameters aren't always the same. Their number can change and the
>>> number of entries can change, and i'd like to have one code that can handle all
>>> configurations.
>>>> 
>>>> Now i thought i could use expand.grid() to get all configurations ,and than iterate over
>>> the rows, but the problem then is that i cannot set the values in the list like above.
>>>> 
>>>> grid<-expand.grid(height,width)
>>>> l[[as.character(grid[1,])]] <-1
>>>> Error in `[[<-`(`*tmp*`, as.character(grid[1, ]), value = 1) :
>>>> no such index at level 1
>>>> 
>>>> This will only work if the "path" for that is already existent, and i'm not sure how to
>>> build that in this scenario.
>>>> 
>>>> I then went on and built an array instead lists of lists, but that doesn't help either
>>> because i can't access the array with what i have in the grids row - or at least i don't
>>> know how.
>>>> 
>>>> Any ideas?
>>>> 
>>>> I'd prefer to keep the named lists since all other code is built towards this.
>>>> ______________________________________________
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>>>> 
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>>> ______________________________________________
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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.

David Winsemius
Alameda, CA, USA