Arrays

An array can be considered as a multiply subscripted collection of data entries, for example numeric. . allows simple facilities for creating and handling arrays, and in particular the special case of matrices.

A dimension vector is a vector of positive integers. If its length is k then the array is k-dimensional. The values in the dimension vector give the upper limits for each of the k subscripts. The lower limits are always 1.

A vector can be used by . as an array only if it has a dimension vector as its dim attribute. Suppose, for example, z is a vector of 1500 elements. The assignment

dim(z) <- c(3,5,100)

gives it the dim attribute that allows it to be treated as a $3\times5\times100$ array.

Other functions such as matrix() and array() are available for simpler and more natural looking assignments, as we shall see in §.

The values in the data vector give the values in the array in the same order as they would occur in Fortran, that is `column major order', with the first subscript moving fastest and the last subscript slowest.

For example if the dimension vector for an array, say a is c(3,4,2) then there are $3\times4\times2=24$ entries in a and the data vector holds them in the order a[1,1,1], a[2,1,1], ..., a[2,4,2], a[3,4,2].