[R] data.frame with a column containing an array

[Bert Gunter]

Right ... that's what I thought you meant.

I'm pretty sure -- but not certain -- that columns of matrices are treated
specially by [.data.frame, so that you have to explicitly index a higher
dimensional array, e.g. like this:


subs <- c(1,3)
DFA <- data.frame(id = 1:3)
DFA[["ar"]] <- array(1:12, c(3,2,2))

DFA$ar[match(subs,DFA$id),,]
##yielding:
, , 1

     [,1] [,2]
[1,]    1    4
[2,]    3    6

, , 2

     [,1] [,2]
[1,]    7   10
[2,]    9   12

You might check, e.g. the "data.table" package, to see if it indexes as you
would like with columns that contain arrays.

Alternatively, and perhaps preferably depending on your use case, you may
wish to create a wholly different data structure or just treat the data
frame as a list from the start. Data frames/matrix-like data structures are
convenient and appropriate a lot of the time, but not always. R, like any
flexible programming language, allows you -- even encourages you -- to
create other data structures that fit your needs.

Cheers,
Bert

On Tue, May 9, 2023 at 3:39 AM Georg Kindermann <Georg.Kindermann using gmx.at>
wrote:

> Thanks!
>
> No, to be consistent with what I get with a matrix I think it should be
> like:
>
> x <- data.frame(id = DFA$id[1])
> x$ar <- DFA$ar[1, , , drop = FALSE]
>
> str(x)
> #'data.frame': 1 obs. of 2 variables:
> # $ id: int 1
> # $ ar: int [1, 1:2, 1:2] 1 3 5 7
>
> Georg
>
>
>
> Gesendet: Dienstag, 09. Mai 2023 um 09:32 Uhr
> Von: "Rui Barradas" <ruipbarradas using sapo.pt>
> An: "Georg Kindermann" <Georg.Kindermann using gmx.at>, r-help using r-project.org
> Betreff: Re: [R] data.frame with a column containing an array
> Às 11:52 de 08/05/2023, Georg Kindermann escreveu:
> > Dear list members,
> >
> > when I create a data.frame containing an array I had expected, that I
> get a similar result, when subsetting it, like having a matrix in a
> data.frame. But instead I get only the first element and not all values of
> the remaining dimensions. Differences are already when creating the
> data.frame, where I can use `I` in case of a matrix but for an array I am
> only able to insert it in a second step.
> >
> > DFA <- data.frame(id = 1:2)
> > DFA[["ar"]] <- array(1:8, c(2,2,2))
> >
> > DFA[1,]
> > # id ar
> > #1 1 1
> >
> > DFM <- data.frame(id = 1:2, M = I(matrix(1:4, 2)))
> >
> > DFM[1,]
> > # id M.1 M.2
> > #1 1 1 3
> >
> > The same when trying to use merge, where only the first value is kept.
> >
> > merge(DFA, data.frame(id = 1))
> > # id ar
> > #1 1 1
> >
> > merge(DFM, data.frame(id = 1))
> > # id M.1 M.2
> > #1 1 1 3
> >
> > Is there a way to use an array in a data.frame like I can use a matrix
> in a data.frame?
> >
> > I am using R version 4.3.0.
> >
> > Kind regards,
> > Georg
> >
> > ______________________________________________
> > R-help using r-project.org mailing list -- To UNSUBSCRIBE and more, see
> > https://stat.ethz.ch/mailman/listinfo/r-help
> > PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html[http://www.R-project.org/posting-guide.html]
> > and provide commented, minimal, self-contained, reproducible code.
> Hello,
>
> Are you looking for something like this?
>
>
> DFA <- data.frame(id = 1:2)
> DFA[["ar"]] <- array(1:8, c(2,2,2))
>
> DFA$ar[1, , ]
> #> [,1] [,2]
> #> [1,] 1 5
> #> [2,] 3 7
>
>
> Hope this helps,
>
> Rui Barradas
>
>
> ______________________________________________
> R-help using r-project.org mailing list -- To UNSUBSCRIBE and more, see
> 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.
>

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