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Source code for networkx.utils.union_find

Union-find data structure.
#    Copyright (C) 2004-2011 by 
#    Aric Hagberg <hagberg@lanl.gov>
#    Dan Schult <dschult@colgate.edu>
#    Pieter Swart <swart@lanl.gov>
#    All rights reserved.
#    BSD license.
import networkx as nx

class UnionFind:
    """Union-find data structure.

    Each unionFind instance X maintains a family of disjoint sets of
    hashable objects, supporting the following two methods:

    - X[item] returns a name for the set containing the given item.
      Each set is named by an arbitrarily-chosen one of its members; as
      long as the set remains unchanged it will keep the same name. If
      the item is not yet part of a set in X, a new singleton set is
      created for it.

    - X.union(item1, item2, ...) merges the sets containing each item
      into a single larger set.  If any item is not yet part of a set
      in X, it is added to X as one of the members of the merged set.

      Union-find data structure. Based on Josiah Carlson's code,
      with significant additional changes by D. Eppstein.


    def __init__(self):
        """Create a new empty union-find structure."""
        self.weights = {}
        self.parents = {}

    def __getitem__(self, object):
        """Find and return the name of the set containing the object."""

        # check for previously unknown object
        if object not in self.parents:
            self.parents[object] = object
            self.weights[object] = 1
            return object

        # find path of objects leading to the root
        path = [object]
        root = self.parents[object]
        while root != path[-1]:
            root = self.parents[root]

        # compress the path and return
        for ancestor in path:
            self.parents[ancestor] = root
        return root
    def __iter__(self):
        """Iterate through all items ever found or unioned by this structure."""
        return iter(self.parents)

[docs] def union(self, *objects): """Find the sets containing the objects and merge them all.""" roots = [self[x] for x in objects] heaviest = max([(self.weights[r],r) for r in roots])[1] for r in roots: if r != heaviest: self.weights[heaviest] += self.weights[r] self.parents[r] = heaviest