[R] reshape dataframe to array (pivot table)

[Johannes Radinger]

Hi Rainer,

thank you for your response.
The combination of melt/cast was what I was looking for.
Now, also the reshape-package and its advantage is a lot clearer
to me.

cheers,
johannes
-------- Original-Nachricht --------
> Datum: Tue, 24 Jan 2012 19:28:43 +0100
> Von: Rainer Schuermann <Rainer.Schuermann at GMX.net>
> An: Johannes Radinger <JRadinger at gmx.at>
> CC: "r-help at r-project.org" <r-help at r-project.org>
> Betreff: Re: [R] reshape dataframe to array (pivot table)

> Hi,
> 
> I wouldn't know how to fill the data into the array form you want, but 
> you can get the aggregated data with
> 
> dfm <- melt( df )
> dfc <- cast( dfm, LOC ~ variable, sum )
>  > dfc
>    LOC SPEC1 SPEC2
> 1   1    23     5
> 2   2    23     2
> 3   3     0     0
> 
> Hope this helps as a first step!
> 
> Rgds,
> Rainer
> 
> 
> On 2012-01-24 17:15, Johannes Radinger wrote:
> > Hello,
> >
> > I would like to reshape a dataframe into an array. This is kind a
> similar task as Excel performs with a Pivot table. To illustrate it:
> >
> > LOC<- factor(c(1,2,2,3,1,1))
> > SPEC1<- c(0,0,23,0,12,11)
> > SPEC2<- c(1,2,0,0,0,4)
> >
> > df<- data.frame(LOC,SPEC1,SPEC2) # original dataframe
> >
> > a<-
> array(NA,dim=c(length(levels(LOC)),1,2),dimnames=list(levels(LOC),"LOC",c("SPEC1","SPEC2"))) #new array set up, how it should look like
> >
> > The final array is splitted by the SPEC (for each SPEC an new layer),
> and
> > the LOC is collapsed so that there is only one line per level of LOC.
> > The array should get populated with:
> > 1) the sums
> > 2) and presence/absence (can be easily calculated from sums)
> >
> > What is the best way to do that? I looked into reshape and
> apply...probably one of them is suitable but I don't know how...Or has that to be done
> with a loop?
> >
> > cheers,
> > /johannes

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