Filling Lists or Arrays of variable dimensions

On Dec 20, 2012, at 10:01 AM, Jessica Streicher wrote:

Really must have been unclear at some point, sorry.

Hasn't it become abundantly clear that this would have progress farther had you post a complete example?

-- 
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
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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.

please

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Thanks,
Saumyha
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