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# Roget

Build a directed graph of 1022 categories and 5075 cross-references as defined in the 1879 version of Roget’s Thesaurus. This example is described in Section 1.2 of

> Donald E. Knuth, “The Stanford GraphBase: A Platform for Combinatorial Computing”, ACM Press, New York, 1993. http://www-cs-faculty.stanford.edu/~knuth/sgb.html

Note that one of the 5075 cross references is a self loop yet it is included in the graph built here because the standard networkx `DiGraph` class allows self loops. (cf. 400pungency:400 401 403 405).

The data file can be found at:

- networkx/networkx

    skipping self loop 400 400
    Loaded roget_dat.txt containing 1022 categories.
    DiGraph with 1022 nodes and 5075 edges
    21 connected components

    import gzip
    import re
    import sys

    import matplotlib.pyplot as plt
    import networkx as nx

    def roget_graph():
        """Return the thesaurus graph from the roget.dat example in
        the Stanford Graph Base.
        """
        # open file roget_dat.txt.gz
        fh = gzip.open("roget_dat.txt.gz", "r")

        G = nx.DiGraph()

        for line in fh.readlines():
            line = line.decode()
            if line.startswith("*"):  # skip comments
                continue
            if line.startswith(" "):  # this is a continuation line, append
                line = oldline + line
            if line.endswith("\\\n"):  # continuation line, buffer, goto next
                oldline = line.strip("\\\n")
                continue

            (headname, tails) = line.split(":")

            # head
            numfind = re.compile(r"^\d+")  # re to find the number of this word
            head = numfind.findall(headname)[0]  # get the number

            G.add_node(head)

            for tail in tails.split():
                if head == tail:
                    print("skipping self loop", head, tail, file=sys.stderr)
                G.add_edge(head, tail)

        return G

    G = roget_graph()
    print("Loaded roget_dat.txt containing 1022 categories.")
    print(G)
    UG = G.to_undirected()
    print(nx.number_connected_components(UG), "connected components")

    options = {
        "node_color": "black",
        "node_size": 1,
        "edge_color": "gray",
        "linewidths": 0,
        "width": 0.1,
    }
    nx.draw_circular(UG, **options)
    plt.show()

Total running time of the script: (0 minutes 0.213 seconds)

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