[R] create an object in a loop (v2)

[David Winsemius]

Upon reading it yesterday, it appeared as it would have required some  
serious testing and there was no data on which to do any work.  You  
were clearly not taking the time to isolate the problem and construct  
a dataset. But who knows? When you say "What I want to do is. ... ,I  
would like the name of the list to be created in the loop too", maybe  
all you needed was to be pointed to was:

?assign

But if that were the case, then you lost most of your audience along  
the way with a bunch of unneeded and obscure code.

-- 
David.


On Feb 1, 2010, at 10:45 AM, Ivan Calandra wrote:

> Hi everybody,
>
> I'm kind of surprised that I didn't get any answer to my question...  
> Is it not interesting? Is it not well explained? Am I doing  
> something wrong? Was it lost in the hundreds of other emails during  
> the weekend?
>
> I hope it is because of my last guess. So I'll just send the email  
> again (see below).
> I really need some help on this matter.
>
> Thanks in advance.
>
>> To run some statistical tests from the package WRS (from Rand R  
>> Wilcox), I need to store my data in a list, which fac2list() from  
>> this package does very well.
>> But I would like to do it in a loop for each numerical variable. It  
>> would be easier!
>>
>> For now, I have the loop with the extraction and storage into a  
>> list. The code is below.
>> -----
>> # Defines variables
>> file <- ssfamed                          #data file object to be used
>> spec <- "cotau"                         #species selection
>> bone <- "tx"                              #tooth row selection
>> cat <- 3                                    #column indexe to be  
>> used as categorical variable
>> seq.num <- c(seq(7,21,1))        #column indexes to be used as  
>> numerical variables
>>
>> # Select data for species and tooth row
>> select <- file[file$SPECSHOR==spec & file$BONE==bone, ]
>>
>> #Separate the data from each numeric variable in seq.num  
>> (select[,k]) into groups from levels in select[cat] and store into  
>> list mode.
>> for(i in 1:length(seq.num)) {
>> k <- seq.num[i]
>> name.num <- names(file)[k]
>> TO_POS_Asfc.median_cotautx <- fac2list(select[,k], select[cat])
>> names(TO_POS_Asfc.median_cotautx) <- levels(factor(select[[cat]]))
>> }
>> -----
>>
>> What I want to do is, instead of giving manually the name of the  
>> list (here TO_POS_Asfc.median_cotautx), I would like the name of  
>> the list to be created in the loop too, so that it looks like:  
>> select[[cat]]_name.num_specbone. In the code it would look like:
>> -----
>> select[[cat]]_name.num_specbone <- fac2list(select[,k],  
>> select[cat])  #create the list from the values of these variables  
>> at each iteration of the loop
>> names(select[[cat]]_name.num_specbone) <-  
>> levels(factor(select[[cat]]))
>> -----
>> I thought about using paste(), but I cannot create an object like  
>> this.
>> In my small R life, I've always stored data into pre-defined  
>> objects, I have no idea how to create an object automatically  
>> within a loop.
>>
>> Is my question clear? I hope so. I thought there might be a  
>> function that would create an object where the name would come from  
>> a string stored in an other object.
>>
>> Why do I want that? Simply because I want to run several  
>> statistical tests on each list and I would therefore like to have  
>> standardized names for the data objects.
>>
>> There might be easier ways to do what I want to, I'm open to all  
>> suggestions but I would prefer to stay close from my idea (I would  
>> understand better!)
>
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> and provide commented, minimal, self-contained, reproducible code.

David Winsemius, MD
Heritage Laboratories
West Hartford, CT