[R] which is the fastest way to make data.frame out of a three-dimensional array?

[Petr Savicky]

On Sat, Feb 25, 2012 at 04:54:30PM +0100, Hans Ekbrand wrote:
> foo <- rnorm(30*34*12)
> dim(foo) <- c(30, 34, 12)
> 
> I want to make a data.frame out of this three-dimensional array. Each dimension will be a variabel (column) in the data.frame.

Hi.

Try this

  n1 <- dim(foo)[1]
  n2 <- dim(foo)[2]
  n3 <- dim(foo)[3]
  df <- cbind(dat=c(foo), expand.grid(dim1=1:n1, dim2=1:n2, dim3=1:n3))
  df[1:5, ]

           dat dim1 dim2 dim3
  1 -0.5765847    1    1    1
  2  0.4490040    2    1    1
  3  0.2626855    3    1    1
  4  0.2206713    4    1    1
  5  0.9079324    5    1    1
  ...

On the contrary to a previous suggestion with foo==foo, this
works also in presence of NA.

Hope this helps.

Petr Savicky.