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.

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.

A vector of character strings specifying column header, defaulting to colnames(x)