arrayhelpers (version 0.75-20111128)

makeNd: Ensure/collapse an array into n dimensions and restore the old dimensions

Description

nameNd ensures a given number of dimensions: If a has less than N dimensions, new dimensions of length 1 are appended. If a has more than N dimensions, the supernumerary dimensions are collapsed onto the last dimension.

Attributes old.dim and old.dimnames are used by default. restoredim is the inverse of makeNd.

Usage

makeNd(a, N)
  restoredim(a, old = NULL, n = 1L, ..., usedim = TRUE,
    fromend = FALSE, drop = FALSE)

Arguments

a

an array (matrix, vector)

N

the desired number of dimensions, 0 to remove the dim and dimnames attributes (i.e. to create a vector).

old

list containing a list with (possibly) elements dim, dimnames, and names. The nth last element of this list is used.

n

how many makeNdim steps to go back?

...

ignored

usedim

use only the specified dimensions

fromend

if TRUE, numeric usedim are counted from the end, see details.

drop

should 1d arrays drop to vectors?

Value

• N-dimensional array

  an array

Details

Note that missing attributes as well as old.dim = NULL produce a (dimensionless) vector. This is also the case if a lost the old.* attributes during computations like as.numeric, c, etc..

fromend together with numeric usedim specifies dimensions counting from the end. E.g. fromend = TRUE and usedim = 1 : 3 for an array to be restored to 10d means restoring dimensions 8 : 10. fromend = TRUE and usedim = -(1 : 3) restores dimensions 1 to 7.

Examples

v <- arrayhelpers:::v
v
makeNd (v, 1)
dim (makeNd (v, 1))
dim (makeNd (v, 3))

m <- arrayhelpers:::m
m
makeNd (m, 1)
dim (makeNd (m, 1))
makeNd (m, 0)
dim (makeNd (m, 0))
makeNd (m, 3)

a <- arrayhelpers:::a
a
dim (makeNd (a, 1))
dim (makeNd (a, 0))
makeNd (a,  2)
makeNd (a, -2)
makeNd (a, -4)
makeNd (a, 3);
a <- array (1 : 24, 4 : 3)
a
restoredim (makeNd (a, 0))

x <- makeNd (a, 0)
attr (x, "old")