Re: [R] melting a list: basic question

From: Dieter Menne <dieter.menne_at_menne-biomed.de>
Date: Fri, 25 Jul 2008 15:35:21 +0000 (UTC)

baptiste auguie <ba208 <at> exeter.ac.uk> writes:

>
> I'm trying to use the reshape package to perform a merging operation
> on a list of data.frames as illustrated below,
>
> > a <- 1:10
> > example <- list( data.frame(a=a, b=sin(a)), data.frame(a=a,
> > b=cos(a)) )
> >
> > melt(example, id = a)
>
> this produces the desired result, where the data.frames have been
> coerced into one with a common identifier variable "a". However, it
> seems that if "a" is of mode numeric it is not recognized as an id
> variable,
>
> > 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



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