This function is the implemtation of the procedure outlined on
http://toreopsahl.com/2009/05/01/projecting-two-mode-networks-onto-weighted-one-mode-networks/
Usage
projecting_tm(net, method = "sum")
Arguments
net
A two-mode edgelist
method
The method-switch control the method used to calculate the weights.
binary sets all weights to 1
sum sets the weights to the number of cooccurances
Newman bases the weights on Newman's (2001) method of discounting for the size of collaborations.