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Note

This documents the development version of NetworkX. Documentation for the current release can be found here.

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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:
['Kasparov, Gary', 'Karpov, Anatoly', 'Korchnoi, Viktor L']

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

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


G = chess_pgn_graph()

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

print(f"Loaded {ngames} chess games between {nplayers} players\n")

# 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 = {game_info["ECO"] for (white, black, game_info) in G.edges(data=True)}
print(f"\nFrom a total of {len(openings)} different 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 ImportError:
    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, font_size=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()