cgroup
A vector or a matrix of character strings defining major column header. The default
is to have none. These elements are also known as column spanners. If you want a column not
to have a spanner then put that column as "". If you pass cgroup and n.crgroup as
matrices you can have column spanners for several rows. See cgroup section below for details.
pos.rowlabel
Where the rowlabel should be positioned. This value can be "top",
"bottom", "header", or a integer between 1 and nrow(cgroup) + 1. The options
"bottom" and "header" are the same, where the row label is presented at the same level as
the header.