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Directed igraph objects

In this exercise you will learn how to create a directed graph from a dataframe, how to inspect whether a graph object is directed and/or weighted and how to extract those vertices at the beginning and end of directed edges.

This exercise is part of the course

Network Analysis in R

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Exercise instructions

  • Convert the dataframe measles into an igraph graph object using the function graph_from_data_frame() and ensure that it will be a directed graph by setting the second argument to TRUE.
  • Check if the graph object is directed by using is.directed().
  • Examine whether the edges of the graph object are already weighted by using is.weighted().
  • Subset each vertex from which each edge originates by using head_of(). This function takes two arguments, the first being the graph object and the second the edges to examine. For all edges you can use E(g).

Hands-on interactive exercise

Have a go at this exercise by completing this sample code.

library(igraph)

# Get the graph object
g <- ___(measles, directed = ___)

# is the graph directed?
___(g)

# Is the graph weighted?
___(g)

# Where does each edge originate from?
table(___(___, E(g)))
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