R help - Jun 2009 - How to append to a list dynamically?

Hi,

I have a problem with dynamic appending to a list. Here is the list
variable:


clusters <- vector("list", 0)


I extended in the function below:


cluster <- function (pair, clusters)
{
  found <- FALSE
  for (i in length(clusters))
  {
    if (length(intersect(pair, clusters[i])) > 0)
    {
     clusters[i] <- union(clusters[i], pair)
     found <- TRUE
    }
  }
  if (!found)
  {
   clusters <- list(clusters, as.vector(pair))
  }
}


The function is executed in a loop:


for (i in 1:nrow(adjMatrix))
{
for (j in 1:nrow(adjMatrix))
{
  if ((i != j) && adjMatrix[i,j] >0) # the matrix element has to be
non-zero
in order to be clustered
  {
    cat(rownames(adjMatrix)[i], colnames(adjMatrix)[j], "\n")
    cluster(as.vector(c(rownames(adjMatrix)[i], colnames(adjMatrix)[j])),
clusters)
  }  
}
}


But the list variable remains empty (i.e. length(clusters) = 0) even though
it should not. Somehow the dynamic extension of the list does not work in
this case. Any suggestions?

Best regards,

Nick
-- 
View this message in context:
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Sent from the R help mailing list archive at Nabble.com.

Function parameters in R are passed by value, not by reference. In
order to resolve it, just remove "clusters" from the parameter list,
and use "clusters[i] <<- ..." to change the value of global
variable.

On Wed, Jun 17, 2009 at 7:52 PM, Nick Angelou<nikolay12 at yahoo.com>
wrote:
>
> Hi,
>
> I have a problem with dynamic appending to a list. Here is the list
> variable:
>
>
> clusters <- vector("list", 0)
>
>
> I extended in the function below:
>
>
> cluster <- function (pair, clusters)
> {
> ?found <- FALSE
> ?for (i in length(clusters))
> ?{
> ? ?if (length(intersect(pair, clusters[i])) > 0)
> ? ?{
> ? ? clusters[i] <- union(clusters[i], pair)
> ? ? found <- TRUE
> ? ?}
> ?}
> ?if (!found)
> ?{
> ? clusters <- list(clusters, as.vector(pair))
> ?}
> }
>
>
> The function is executed in a loop:
>
>
> for (i in 1:nrow(adjMatrix))
> {
> for (j in 1:nrow(adjMatrix))
> {
> ?if ((i != j) && adjMatrix[i,j] >0) # the matrix element has to
be non-zero
> in order to be clustered
> ?{
> ? ?cat(rownames(adjMatrix)[i], colnames(adjMatrix)[j], "\n")
> ? ?cluster(as.vector(c(rownames(adjMatrix)[i], colnames(adjMatrix)[j])),
> clusters)
> ?}
> }
> }
>
>
> But the list variable remains empty (i.e. length(clusters) = 0) even though
> it should not. Somehow the dynamic extension of the list does not work in
> this case. Any suggestions?
>
> Best regards,
>
> Nick
> --
> View this message in context:
http://www.nabble.com/How-to-append-to-a-list-dynamically--tp24071794p24071794.html
> Sent from the R help mailing list archive at Nabble.com.
>
> ______________________________________________
> 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.
>

On Jun 17, 2009, at 7:52 AM, Nick Angelou wrote:
> I have a problem with dynamic appending to a list. Here is the list
> variable:
>
>
> clusters <- vector("list", 0)
>
  library(fortunes)
  fortune("dog")

I would suggest that referring to a character vector as a "list", and
then also calling an element in that vector "list" is akin to calling
your cat, "dog", and then calling its tail, "dog", as well.
>
> I extended in the function below:
>
>
> cluster <- function (pair, clusters)
> {
>  found <- FALSE
>  for (i in length(clusters))
>  {
>    if (length(intersect(pair, clusters[i])) > 0)
>    {
>     clusters[i] <- union(clusters[i], pair)
>     found <- TRUE
>    }
>  }
>  if (!found)
>  {
>   clusters <- list(clusters, as.vector(pair))
So the first time cluster() is called, it would need to handle a  
vector correctly, but now you have changed clusters to be a list and  
the second call to clusters will need to handle a list correctly.
>  }
> }
>
>
> The function is executed in a loop:
>
>
> for (i in 1:nrow(adjMatrix))
> {
> for (j in 1:nrow(adjMatrix))
> {
>  if ((i != j) && adjMatrix[i,j] >0) # the matrix element has to
be
> non-zero
> in order to be clustered
>  {
>    cat(rownames(adjMatrix)[i], colnames(adjMatrix)[j], "\n")
>    cluster(as.vector(c(rownames(adjMatrix)[i], colnames(adjMatrix) 
> [j])),
> clusters)
>  }
> }
> }
>
>
> But the list variable remains empty (i.e. length(clusters) = 0) even  
> though
> it should not. Somehow the dynamic extension of the list does not  
> work in
> this case. Any suggestions?
Use appropriate naming and do not conflate "vector" with
"list". They
need different functions to properly access elements or extend their  
lengths.

David Winsemius, MD
Heritage Laboratories
West Hartford, CT