Filling Lists or Arrays of variable dimensions

l[[ as.character(grid[1, ]) ]] <- 1

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
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Chippenham
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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.

please

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