Creates a sgldata data object from a matrix or vector
prepare_data(x, default = NULL, type = "numeric", sparse = is(x,
"sparseMatrix"))the matrix,
default value, returned if x is null
data type, 'numeric' or 'integer'
if TRUE y will be treated as sparse, if FALSE y will be treated as dens.
Other sgldata: add_data.sgldata,
create.sgldata,
prepare.args.sgldata,
prepare.args,
rearrange.sgldata,
subsample.sgldata