## Usage

ra4(speciesData = matrix(rpois(80, 1), nrow = 10))

## Arguments

- speciesData
- a resource utilization matrix (rows = species, columns = discrete
resource states) filled with non-negative real numbers.

## Value

Returns a random utilization matrix with the same dimensions as the
input matrix.

## Description

Randomizes a numeric utilization matrix speciesData by
reshuffling the non-zero elements within each row.

## Details

The resource utilization matrix (rows = species, columns = discrete
resource categories) may include zeroes, but no negative numbers or missing
values. Relative resource within a species is first calculated, so the rows
need not sum to 1.0.

## Note

This algorithm is similar to RA3, but adds the additional constraint of
retaining the positions of all of the zero elements of the matrix, and
reshuffling only the non-zero elements of the matrix within each row. It is
more conservative than RA3, but has a low Type I error rate, and, along with
RA3, is recommended for null model analysis of niche overlap.

## References

Winemiller, K.O. and E.R. Pianka. 1990. Organization in natural
assemblages of desert lizards and tropical fishes. Ecological Monographs
60: 27-55.

## Examples

ranUtil <- ra4(speciesData=matrix(rpois(40,0.5),nrow=8))

**Warning message:
number of items to replace is not a multiple of replacement length**