R help - Sep 2010 - Data.frames : difference between x$a and x[, "a"] ? - How set new values on x$a with a as variable ?

Hi,

I got two questions :

1st Question
            a="S"
            b=data.frame(S=3)
            do.call(`<-`,list(do.call(`$`,list(b,"S")),5))
=> How can I put new values on S column having the column name as a variable
?

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 ?


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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Hi

r-help-bounces at r-project.org napsal dne 10.09.2010 10:05:37:
> Hi,
> 
> I got two questions :
> 
> 1st Question
> ? ? ?  ? ? ?  ? ? ?  a="S"
> ? ? ?  ? ? ?  ? ? ?  b=data.frame(S=3)
> ? ? ?  ? ? ?  ? ? ? 
do.call(`<-`,list(do.call(`$`,list(b,"S")),5))
> => How can I put new values on S column having the column name as a 
variable ?
> 
> 2 nd Question
> ? ? ? ? ? ?  a="S"
> ? ? ?  ? ?  b=data.frame(S=3)
> ? ?  ? ? ?  b[,"S"]=list(1:10) #Doesnt works
> ? ?  ? ? ?  b$S=list(1:10) #Works
> => Isnt the same thing ? What is the difference between these two things
?

did you looked at b e.g. by str(b)? I believe you expected something 
different.

Maybe you wanted rbind
rbind(b[,"S"],data.frame(S=1:10))

Regards
Petr
> 
> 
> Thanks,
> 
> Une messagerie gratuite, garantie ?  vie et des services en plus, ??a 
vous tente ?
> Je cr??e ma bo??te mail www.laposte.net
> 
>    [[alternative HTML version deleted]]
> 
> ______________________________________________
> 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.

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 ? vie et des services en plus, ?a vous
tente ?
> Je cr?e ma bo?te mail www.laposte.net
>
> ? ? ? ?[[alternative HTML version deleted]]
>
>
> ______________________________________________
> 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.
>
>


-- 
Ista Zahn
Graduate student
University of Rochester
Department of Clinical and Social Psychology
http://yourpsyche.org