check_weights is a helper function for dealing with edge weights that
get passed to different igraph functions.
check_degree is a helper function to check if degree is a
vertex attribute of the input graph. Returns a numeric vector of the degree
values.
check_strength is a helper function to check if strength is a
vertex attribute of the input graph. Returns a numeric vector of the strength
values.
check_weights(g, weights)check_degree(g)
check_strength(g)
check_weights - If weights=NULL and the graph has a
'weight' attribute, then NULL will be returned. If
weights=NA, then NA is returned.