Global Variable declaration and accessing in R

Question

I'm having a dataframe in which I'm reading from a test file as like below

    Country,count
    uk,34
    au,35
    us,53
    in,44

This is my R script. This is just an example. When I'm trying to access a dataframe variable outside the loop which get created inside the for loop , I'm getting object not found error. Even I tried using assign. Getting the same error. I'm using R version 2.15.1.

    args <- commandArgs()
    #Storing the filename in fn given next to "--args"
    fn <- args[which(args=="--args")+1]
    t<-read.table(fn,sep=",",header=TRUE,as.is=TRUE,quote="")
    t
    for (i in levels(t$Country)){
            if ( i == us ) {
            RES <<- t[t$Country == i,]
            }
    }
    RES

    > args <- commandArgs()
    > #Storing the filename in fn given next to "--args"
    > fn <- args[which(args=="--args")+1]
    > t<-read.table(fn,sep=",",header=TRUE,as.is=TRUE,quote="")
    > t
      Country count
    1      uk    34
    2      au    35
    3      us    53
    4      in    44
    > for (i in levels(t$Country)){
    +       if ( i == us ) {
    +       RES <<- t[t$Country == i,]
    +       }
    + }
    > RES
    Error: object 'RES' not found
    Execution halted

I belive, I'm doing something wrong. Please advise.

<<- is to declare/access a variable globally.. Also <- is not working. — Tamilan
– Tamilan, Commented Sep 13, 2012 at 13:14
In my example I should have put as "us". replaced levels with unique works fine in my real scenario. Thank you.. — Tamilan
– Tamilan, Commented Sep 13, 2012 at 15:26

Michael · Accepted Answer · 2012-09-13 13:25:25Z

2

Most of the chances the if constraint is never met (i == us)

it will never be equal to us. try to remove the "levels"

 for (i in t$Country)
      if (i =="us")

edited Sep 13, 2012 at 13:25

answered Sep 13, 2012 at 13:19

Michael

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1 Comment

Tamilan Over a year ago

I replaced levels with unique(t$Country) it is working fine now.. Thank you very much for your great hint..

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