

Le 9/10/2010 15:37, Ista Zahn a écrit :
> On Fri, Sep 10, 2010 at 9:22 AM, omerle<omerle@laposte.net>  wrote:
>>> Message du 10/09/10 14:53
>>> De : "Ista Zahn"
>>> A : "omerle"
>>> Copie à : r-help@r-project.org
>>> Objet : Re: [R] Data.frames : difference between x$a and x[, "a"] ? - How set new values on x$a with a as variable ?
>>>
>>>
>>> Hi,
>>>
>>> On Fri, Sep 10, 2010 at 4:05 AM, omerle wrote:
>>>> Hi,
>>>>
>>>> I got two questions :
>>>>
>>>> 1st Question
>>>>              a="S"
>>>>              b=data.frame(S=3)
>>>>              do.call(`<-`,list(do.call(`$`,list(b,"S")),5))
>>> I think there is some confusion here. Why are you setting a equal to
>>> "S" but then never using it?
>>>
>>>> =>  How can I put new values on S column having the column name as a variable ?
>>> I'm having trouble parsing this. What exactly do you want to do?
>> 1 - Put a list as an element of a data.frame. That's quite convenient for my pricing function.
> I think this is a really bad idea. data.frames are not meant to be
> used in this way. Why not use a list of lists?
Since data.frames are lists, why would it be a bad practice?
>>>> 2 nd Question
>>>>         a="S"
>>>>         b=data.frame(S=3)
>>>>         b[,"S"]=list(1:10) #Doesnt works
>>>>         b$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.
>> 2 - That's what I want. I figured out just five minutes ago that b[["S"]] works because it's the same thing as b$S.
>> But I still dont know what is b[,"S"] compared to b[["S"]]
> see ?"["
 From the help page, there is not much distinction. Maybe I haven't 
understood all the details...

Ivan

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Ivan CALANDRA
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