[R] Assigning objects to variable and variable to list in a for loop

[Johannes Radinger]

Hello,

I tried to use the lapply approach, but I am not sure how to 
se it correctly for my task. Here I just want to give an short
script which explains how my data structure looks like. It also
contains the second approach with a for loop which is working but
there is the question of how assining the result to a list.

I think the script is somehow self explaining. Anyway what is called
res is in "reality" rather an object (maxent) than a single value (thats why I need the list)

#create data
cat <- c("A","A","B","C","C")
value <- runif(5)
df <- data.frame(cat,value)

# get names of cat with more than 1 entries
select.cat <- names(table(df$cat)[table(df$cat)>1])
cat.list <- as.list(select.cat)

###### lapply approach ####
fun = function(x){
	sub.df<- subset(df,cat ==  x)
	# here are other operations, result is an object
	res <- sub.df
	res #here just a single value but in the long script it is an object
	}	
reslist <- lapply(cat.list, fun(unlist(cat.list)))

###### For loop approach ####
for(i in select.cat){
	sub.df<- subset(df,cat ==  i)
	res <- sub.df
	print(res) #here just a single value but in the long script it is an object
	#Now I have to collect the results in a list
	}

# My task is to do run a function on different parts
#of a dataframe. This dataframe is subdivided with subset on
#one variable.


Thank you very much,

best regards,

Johannes

-------- Original-Nachricht --------
> Datum: Fri, 3 Feb 2012 02:22:30 -0800
> Von: Joshua Wiley <jwiley.psych at gmail.com>
> An: Johannes Radinger <JRadinger at gmx.at>
> CC: r-help at r-project.org
> Betreff: Re: [R] Assigning objects to variable and variable to list in a for loop

> Hi Johannes,
> 
> There is a relatively elegant solution if you assign in a list:
> 
> reslist <- lapply(1:3, function(x) runif(5))
> names(reslist) <- paste("result", LETTERS[1:3], sep = "_")
> 
> Cheers,
> 
> Josh
> 
> On Fri, Feb 3, 2012 at 2:07 AM, Johannes Radinger <JRadinger at gmx.at>
> wrote:
> > Hello,
> >
> > I want to use a for loop for repeadely calculating
> > a maxent model (package dismo, function maxent()) which
> > creates an object of the class maxent (S4).
> > I want to collect all the resulting object in a list.
> >
> > I tried to simplify my for loop to explain what I want.
> > There are two problems/questions:
> > 1) How can I create the new variables in the loop (using paste) and
> assign the objects
> > 2) How can I collect the results (objects) in a list
> >
> > X <- factor(c("A","B","C"))
> >
> > for(in in X){
> >        as.name(paste("result","X",sep="_")) <- runif(5) #any object
> >        # create list of objects with names
> >        }
> >
> > I read something about assign(), but that assigns a value and not an
> object to a variable. Some time ago I did something similar but with a matrix:
> Thus I created an empty matrix before the loop and indexed the matrix
> inside the loop to assign values. But here it is about assigning ojects to
> variables and coercing these to a list.
> >
> > Any suggestions are mostly welcomme.
> >
> > Thank you,
> >
> > best regards,
> > Johannes Radinger
> > --
> >
> > ______________________________________________
> > 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.
> 
> 
> 
> -- 
> Joshua Wiley
> Ph.D. Student, Health Psychology
> Programmer Analyst II, Statistical Consulting Group
> University of California, Los Angeles
> https://joshuawiley.com/

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