[R] melting a list: basic question

[baptiste auguie]

Given that I cannot arbitrarily change the data to make "a" an  
integer, can I still use "a" as a grouping variable?

I tried melt(example, id = factor(a)) but it does not work either.  
Must this change from numeric values to factors be done before  
applying melt?

Thanks,

baptiste

On 25 Jul 2008, at 16:35, Dieter Menne wrote:

>>
>>
>>> a <- as.numeric(1:10)
>>>
>>> example <- list(data.frame(a=a, b=sin(a)), data.frame(a=a,  
>>> b=cos(a)))
>>>
>>> melt(example, id = a) # this does not use a as an id variable
>>
>
> This is the documented behavior: Only integers and factors are used  
> for
> grouping, but as.numeric is double, even if 1:10 looks like integers
>
> a <- as.integer(1:10)
> or simply
>
> a <- 1:10
>
> Dieter