Creates a matrix or three dimensional array of sparse data with NAs from a list of sparse data. The number of columns of the matrix will be equal to the length of the list (replications)
sparse.mat(datalist)
A list object. Each element must be a matrix object where the rows correspond to argument values per individual. First column corresponds to time points and the following columns to argument values per variable.
a matrix or array with ncol = length(datalist). First dimension corresponds to point observations, second dimension corresponds to replications and third dimension corresponds to variables.