[R] recovering collums of DF using a text var.list

[Petr Klasterecky]

Milton Cezar Ribeiro napsal(a):
> Hello people,
> 
> I would like to know how can I use a list of variables (a char list) to have access to the collums from a dataframe to be used in some analysis like, just as example, a ploting task on a "for()" loop. Of course the code below is just to understand the way. In this example I have a dataframe with several collumns (more then fifty in my case) and I would like do use only some of them. I really need use a "var.list"! 
> 
> a<-seq(1,100,1)
> b<-c(rep(c(1,2,3,4,5),20))
> c<-rnorm(100,0,1)
> d<-runif(100,0,1)
> e<-c^2
> f<-c/d
> g<-c-d
> df<-data.frame(cbind(a,b,c,d,e,f,g))
> var.list<-c("c","f","g")
> for (myvar in var.list) 
>  {
>  plot(density(df$myvar))   # here I need recover df$c , df$f and df$g
>  }
> 
> Kind regards
> Miltinho 
> Brazil
> 
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Is this what you expect?
for (myvar in var.list) {
plot(density(df[[paste(myvar)]]), main=paste('Density of',myvar))
}

It may not be bad idea to make a structure (list, dataframe) consisting 
of only those variables you want and use some variant of apply() instead 
of the for-loop. See ?apply, ?tapply, ?sapply

Petr
-- 
Petr Klasterecky
Dept. of Probability and Statistics
Charles University in Prague
Czech Republic