[R] Assignment to variables fails to loop

[baptiste auguie]

The variable name in your call to assign should vary within the for  
loop, otherwise you're always assigning the value to the same variable.

Consider the following example,

> listOfNames <- c("a", "b", "c")
> listOfVariables <- c("vara", "varb", "varc")
>
> for(index in seq_along(listOfNames)){
>
> 	print(index) # integer sweeping the two lists
> 	print(paste("assigning variable", listOfNames[index], "to ",  
> listOfVariables[index]))
> 	assign(listOfNames[index], listOfVariables[index])
>
> }
>
>
> # or more succinctly
> mapply(assign, x=listOfNames, value=listOfVariables)

HTH,

baptiste


On 27 Mar 2009, at 18:11, Steve Murray wrote:

>
> Dear all,
>
> I think I'm nearly there in writing R code which will read in files  
> with two variable parts to the file name and then assigning these  
> file names to objects, which also have two variable parts. I have  
> got the code running without encountering errors, however, I receive  
> 50+ of the same warnings:
>
> 1: In assign(paste("Fekete_", index$year, index$month, sep =  
> ""),  ... :
>  only the first element is used as variable name
>
> And it's true, when I do ls() only Fekete198601 has been assigned.  
> I've attempted to rectify this, but have only come up against  
> further errors.
>
> The code as it stands, is as follows:
>
>
> # READ IN FILES FROM DISK
>
> # File names have two variable parts: creating a 'file index' is a  
> two-step process
>
> index <- expand.grid(year = sprintf("%04d", seq(1986, 1995)), month  
> = sprintf("%02d", 1:12))
> filelist <- paste("C:\\Documents and Settings\\Data\ 
> \comp_runoff_hd_", paste(index$year, index$month, sep=''), '.asc',  
> sep='')
>
> filelist
>
>
> # Assign file names to individual objects with variable name  
> components
>
> for (i in filelist) {
>          assign(paste("Fekete_",index$year, index$month,  
> sep=''),read.table(file=i, header=FALSE, sep=" "))
>
>
>          update <- substr(i,35,55) # substring - 2nd argument is  
> character at which extraction is to begin, 3rd argument is where  
> extraction ends.
>          print(c("LOADED FILE:",update), quote=FALSE)
>          }
>
>
>> ls()
> [1] "Fekete_198601" "filelist"      "i"             "index"
> [5] "update"
>
>
> Why is it that only Fekete_198601 has had data assigned to it (there  
> should be 120 such objects in total) and how do I go about solving  
> this?
>
>
> Many thanks again for any help offered,
>
>
> Steve
>
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> and provide commented, minimal, self-contained, reproducible code.

_____________________________

Baptiste Auguié

School of Physics
University of Exeter
Stocker Road,
Exeter, Devon,
EX4 4QL, UK

Phone: +44 1392 264187

http://newton.ex.ac.uk/research/emag