Create the node attribute slot that the Bioconductor graph class
requires, including a default value, and then specifying what the base
type (or 'class') is -- 'char', 'integer', or 'numeric' -- which is needed by
RCy3. This method converts these standard R data type names, to
the forms needed by Cytoscape.
# first, delete existing windows to save memory: deleteAllWindows(CytoscapeConnection())
g = new ('graphNEL', edgemode='directed')
g = initNodeAttribute (g, 'lfc', 'numeric', 1.0)