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Chess Masters

An example of the MultiDiGraph clas

The function chess_pgn_graph reads a collection of chess matches stored in the specified PGN file (PGN =”Portable Game Notation”). Here the (compressed) default file:

chess_masters_WCC.pgn.bz2

contains all 685 World Chess Championship matches from 1886–1985. (data from http://chessproblem.my-free-games.com/chess/games/Download-PGN.php)

The chess_pgn_graph() function returns a MultiDiGraph with multiple edges. Each node is the last name of a chess master. Each edge is directed from white to black and contains selected game info.

The key statement in chess_pgn_graph below is:

G.add_edge(white, black, game_info)

where game_info is a dict describing each game.

Out:

Loaded 685 chess games between 25 players

Note the disconnected component consisting of:
['Karpov, Anatoly', 'Korchnoi, Viktor L', 'Kasparov, Gary']

From a total of 237 different openings,
the following games used the Sicilian opening
with the Najdorff 7...Qb6 "Poisoned Pawn" variation.

Spassky, Boris V vs Fischer, Robert J
    Event :  World Championship 28th
    Site :  Reykjavik ISL
    Date :  1972.07.25
    Round :  7
    Result :  1/2-1/2
    WhiteElo :  2660
    BlackElo :  2785
    ECO :  B97
    EventDate :  1972.07.11


Spassky, Boris V vs Fischer, Robert J
    Event :  World Championship 28th
    Site :  Reykjavik ISL
    Date :  1972.08.06
    Round :  11
    Result :  1-0
    WhiteElo :  2660
    BlackElo :  2785
    ECO :  B97
    EventDate :  1972.07.11

#    Copyright (C) 2006-2019 by
#    Aric Hagberg <hagberg@lanl.gov>
#    Dan Schult <dschult@colgate.edu>
#    Pieter Swart <swart@lanl.gov>
#    All rights reserved.
#    BSD license.

import matplotlib.pyplot as plt
import networkx as nx

# tag names specifying what game info should be
# stored in the dict on each digraph edge
game_details = ["Event",
                "Date",
                "Result",
                "ECO",
                "Site"]


def chess_pgn_graph(pgn_file="chess_masters_WCC.pgn.bz2"):
    """Read chess games in pgn format in pgn_file.

    Filenames ending in .gz or .bz2 will be uncompressed.

    Return the MultiDiGraph of players connected by a chess game.
    Edges contain game data in a dict.

    """
    import bz2
    G = nx.MultiDiGraph()
    game = {}
    datafile = bz2.BZ2File(pgn_file)
    lines = (line.decode().rstrip('\r\n') for line in datafile)
    for line in lines:
        if line.startswith('['):
            tag, value = line[1:-1].split(' ', 1)
            game[str(tag)] = value.strip('"')
        else:
            # empty line after tag set indicates
            # we finished reading game info
            if game:
                white = game.pop('White')
                black = game.pop('Black')
                G.add_edge(white, black, **game)
                game = {}
    return G


if __name__ == '__main__':
    G = chess_pgn_graph()

    ngames = G.number_of_edges()
    nplayers = G.number_of_nodes()

    print("Loaded %d chess games between %d players\n"
          % (ngames, nplayers))

    # identify connected components
    # of the undirected version
    H = G.to_undirected()
    Gcc = [H.subgraph(c) for c in nx.connected_components(H)]
    if len(Gcc) > 1:
        print("Note the disconnected component consisting of:")
        print(Gcc[1].nodes())

    # find all games with B97 opening (as described in ECO)
    openings = set([game_info['ECO']
                    for (white, black, game_info) in G.edges(data=True)])
    print("\nFrom a total of %d different openings," % len(openings))
    print('the following games used the Sicilian opening')
    print('with the Najdorff 7...Qb6 "Poisoned Pawn" variation.\n')

    for (white, black, game_info) in G.edges(data=True):
        if game_info['ECO'] == 'B97':
            print(white, "vs", black)
            for k, v in game_info.items():
                print("   ", k, ": ", v)
            print("\n")

    # make new undirected graph H without multi-edges
    H = nx.Graph(G)

    # edge width is proportional number of games played
    edgewidth = []
    for (u, v, d) in H.edges(data=True):
        edgewidth.append(len(G.get_edge_data(u, v)))

    # node size is proportional to number of games won
    wins = dict.fromkeys(G.nodes(), 0.0)
    for (u, v, d) in G.edges(data=True):
        r = d['Result'].split('-')
        if r[0] == '1':
            wins[u] += 1.0
        elif r[0] == '1/2':
            wins[u] += 0.5
            wins[v] += 0.5
        else:
            wins[v] += 1.0
    try:
        pos = nx.nx_agraph.graphviz_layout(H)
    except:
        pos = nx.spring_layout(H, iterations=20)

    plt.rcParams['text.usetex'] = False
    plt.figure(figsize=(8, 8))
    nx.draw_networkx_edges(H, pos, alpha=0.3, width=edgewidth, edge_color='m')
    nodesize = [wins[v] * 50 for v in H]
    nx.draw_networkx_nodes(H, pos, node_size=nodesize, node_color='w', alpha=0.4)
    nx.draw_networkx_edges(H, pos, alpha=0.4, node_size=0, width=1, edge_color='k')
    nx.draw_networkx_labels(H, pos, fontsize=14)
    font = {'fontname': 'Helvetica',
            'color': 'k',
            'fontweight': 'bold',
            'fontsize': 14}
    plt.title("World Chess Championship Games: 1886 - 1985", font)

    # change font and write text (using data coordinates)
    font = {'fontname': 'Helvetica',
            'color': 'r',
            'fontweight': 'bold',
            'fontsize': 14}

    plt.text(0.5, 0.97, "edge width = # games played",
             horizontalalignment='center',
             transform=plt.gca().transAxes)
    plt.text(0.5, 0.94, "node size = # games won",
             horizontalalignment='center',
             transform=plt.gca().transAxes)

    plt.axis('off')
    plt.show()