graph_attr_dt is a helper function that takes a brainGraphList
or a list of graphs and creates a data.table of global measures for
each graph. Each row will be for a different graph.
vertex_attr_dt is a helper function that creates a data.table
in which each row is a vertex and each column is a different network measure
(degree, centrality, etc.).
graph_attr_dt(bg.list)vertex_attr_dt(bg.list)
A data.table
A brainGraphList object, or a list of graph objects