[R] Data.frames : difference between x$a and x[, "a"] ? - How set new values on x$a with a as variable ?

[Ista Zahn]

Hi,

On Fri, Sep 10, 2010 at 4:05 AM, omerle <omerle at laposte.net> wrote:
> Hi,
>
> I got two questions :
>
> 1st Question
>             a="S"
>             b=data.frame(S=3)
>             do.call(`<-`,list(do.call(`$`,list(b,"S")),5))

I think there is some confusion here. Why are you setting a equal to
"S" but then never using it?

> => How can I put new values on S column having the column name as a variable ?

I'm having trouble parsing this. What exactly do you want to do?

>
> 2 nd Question
>        a="S"
>        b=data.frame(S=3)
>        b[,"S"]=list(1:10) #Doesnt works
>        b$S=list(1:10) #Works
> => Isnt the same thing ? What is the difference between these two things ?

I believe b[["S"]] is the same as b$S, b[,"S"] is different. But I
have to question your assertion that b$S=list(1:10) "Works". This is a
very odd construction (putting a list as an element of a data.frame)
and is almost certainly not what you want.

>
>
> Thanks,
>
> Une messagerie gratuite, garantie à vie et des services en plus, ça vous tente ?
> Je crée ma boîte mail www.laposte.net
>
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-- 
Ista Zahn
Graduate student
University of Rochester
Department of Clinical and Social Psychology
http://yourpsyche.org