R help - Jun 2012 - Add a dim to an array

Dear list,

I'm trying to add a new dim to a multidimensional array. My array looks 
like this

a1 <- array(1:8, c(2, 2, 2))
dimnames(a1) <- list(A = c("A1", "A2"),
                      B = c("B1", "B2"),
                      D = c("D1", "D2"))

I would like to add a new dim 'group' with the value "low".
Right now
I'm using this, but I think are better ways...

a2 <- as.data.frame(as.table(a1))
a2$group <- "low"
a2 <- xtabs(Freq ~ A + B + D + group, data = a2)
a2

Thanks for any help!
Patrick

Hello,

Try

a3 <- array(dim=c(2, 2, 2, 2))
dn <- dimnames(a1)
dn$group <- c("low", "high")
dimnames(a3) <- dn
a3[] <- a1  # to use [] keeps the dimensions
a3          # it fills a3 recycling a1 (two copies)

dim(a2)
dim(a3)


As you can see, 'a2' is not of the right dimensions, and 'a3'
has now
two copies of 'a1' but it's dimensions are right.
There are ways of giving dimnames to 'a3' other than creating a new 
object, 'dn', but this one is a simple one.

Hope this helps,

Rui Barradas

Em 02-06-2012 16:17, Patrick Hausmann escreveu:
> Dear list,
>
> I'm trying to add a new dim to a multidimensional array. My array 
> looks like this
>
> a1 <- array(1:8, c(2, 2, 2))
> dimnames(a1) <- list(A = c("A1", "A2"),
>                      B = c("B1", "B2"),
>                      D = c("D1", "D2"))
>
> I would like to add a new dim 'group' with the value
"low". Right now
> I'm using this, but I think are better ways...
>
> a2 <- as.data.frame(as.table(a1))
> a2$group <- "low"
> a2 <- xtabs(Freq ~ A + B + D + group, data = a2)
> a2
>
> Thanks for any help!
> Patrick
>
> ______________________________________________
> R-help at r-project.org mailing list
> 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.

On Sat, Jun 02, 2012 at 05:17:36PM +0200, Patrick Hausmann
wrote:
> Dear list,
> 
> I'm trying to add a new dim to a multidimensional array. My array looks
> like this
> 
> a1 <- array(1:8, c(2, 2, 2))
> dimnames(a1) <- list(A = c("A1", "A2"),
>                      B = c("B1", "B2"),
>                      D = c("D1", "D2"))
> 
> I would like to add a new dim 'group' with the value
"low". Right now
> I'm using this, but I think are better ways...
> 
> a2 <- as.data.frame(as.table(a1))
> a2$group <- "low"
> a2 <- xtabs(Freq ~ A + B + D + group, data = a2)
> a2
Hi.

Try the following.

  a1 <- array(1:8, c(2, 2, 2))
  dimnames(a1) <- list(A = c("A1", "A2"),
                       B = c("B1", "B2"),
                       D = c("D1", "D2"))
  a2 <- array(a1, c(2, 2, 2, 1))
  dimnames(a2) <- c(dimnames(a1), list(group = "low"))
  a2

  , , D = D1, group = low
  
      B
  A    B1 B2
    A1  1  3
    A2  2  4
  
  , , D = D2, group = low
  
      B
  A    B1 B2
    A1  5  7
    A2  6  8

Hope this helps.

Petr Savicky.