Q:

Graph that average degree node is 4 in R

How can i create a random graph that average node degree is 4? 
After creating a random graph ,how can i find how many links are in the graph?
I found a function for K-Nearest Neighbor Graph , is there any function for average node degree?
    library (igraph)
    g4 <- random.graph.game(100, p=5/100)
    graph.knn(g4)
    degree.distribution(g4)

A:

There is no need for that function, R is pretty good at calculating averages:
mean(degree(g4))
# [1] 4.58

The number of edges is reported by ecount:
ecount(g4)
# [1] 229

To generate a random graph that has average degree 4, you can use G(n,m) graphs. If these satisfy your needs, you can generate them using random.graph.game:
g5 <- random.graph.game(10, 10 * 4 / 2, type="gnm")
mean(degree(g5))
# [1] 4

