[R] Building a list

[jim holtman]

Let initialize Chain:

Chain <- vector('list', 5)
groups <- 1:5
for(j in 1:10000){

   for(g in groups){

       coef <- c(1,2,3,4,5,6,7,8,9,10) #would be actual MCMC samples

       Chain[[g]] <- rbind(Chain[[g]], coef)
   }
}


On Sun, May 30, 2010 at 6:05 PM, Noah Silverman <noah at smartmediacorp.com> wrote:
> That would be great, except I just realized I made a typo when sending
> my code.
>
> I'm tracking 20 coefficents for 10 groups.  So I need a "top" list of 10
> groups.  Then each of the 10,000 samples for each of the 20 coefficients.
>
> It should be more like this:
>
> for(j in 1:10000){
>    for(g in groups){
>        coef <- c(1,2,3,4,5,6,7,8,9,10) #would be actual MCMC samples
>        Chain[[g]] <- rbind(Chain[[g]], coef)
>    }
> }
>
> So, there are 10 lists in "Chain"  (One for each group.)  Each list is
> then a matrix/data.frame of values for each coef.  (Hence the "rbind" in
> my code.)
>
> R gives me an error about the subscript, as Chain[[g]] is empty for the
> first iteration.
>
>
>
>
> On 5/30/10 3:00 PM, Joshua Wiley wrote:
>> Hello Noah,
>>
>> Does this work for you?
>>
>> Chain <- vector("list", 10000)
>> for (j in 1:10000){
>>    coef <- c(1,2,3,4,5,6,7,8,9,10)  #would be actual MCMC samples
>>    Chain[[j]] <- rbind(Chain[[j]], coef)
>>
>> If it does, this has the additional advantage that it tends to be
>> faster to initialize the list at size rather than expanding it as
>> needed.
>>
>> HTH,
>>
>> Josh
>>
>> On Sun, May 30, 2010 at 2:52 PM, Noah Silverman <noah at smartmediacorp.com> wrote:
>>
>>> Hello,
>>>
>>> I need to build a "list of lists"
>>>
>>> We have 20 groups we are generating MCMC samples for.  There are 10
>>> coefficients, and 10000 MCMC iterations.
>>>
>>> I would like to store each iteration by-group in a list.  My problem is
>>> with the first iteration.
>>>
>>> Here is a toy example:
>>>
>>> Chain <- list()
>>> for (j in 1:10000){
>>>    coef <- c(1,2,3,4,5,6,7,8,9,10)  #would be actual MCMC samples
>>>    Chain[[j]] <- rbind(Chain[[j]], coef)
>>> }
>>>
>>> This returns an error, UNLESS I  initialize the first row of Chain[[j]]
>>> with something.
>>>
>>> The idea is that for any group, I can quickly extract, plot, average,
>>> etc the values for each coefficient.
>>>
>>> for example:
>>>
>>> Chain[[5]][,3] will give me all 10,000 values of coefficient 3 for group
>>> 5.
>>>
>>> Again, this seems to work, but I can't initialize the chain with a
>>> random value as it will cause problems with the data summary later.
>>> (Each row in Chain[[j]] will be out of sync by 1, subsequently all
>>> summary and plotting work will have to account for this - it can get
>>> messy in a large program.)
>>>
>>> Is there an easier way to do this?  Am I missing something?
>>>
>>> ______________________________________________
>>> 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.
>>>
>>>
>>
>>
>>
>
> ______________________________________________
> 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.
>



-- 
Jim Holtman
Cincinnati, OH
+1 513 646 9390

What is the problem that you are trying to solve?