A set union find algorithm

Question

I have thousands of lines of 1 to 100 numbers, every line define a group of numbers and a relationship among them. I need to get the sets of related numbers.

Little

Answer 1

You can model a group using a set. In the example below, I've put the set into a Group class to make it easier to keep references to them and to track some notional 'head' item.

class Group:
    def __init__(self,head):
        self.members = set()
        self.head = head
        self.add(head)
    def add(self,member):
        self.members.add(member)
    def union(self,other):
        self.members = other.members.union(self.members)

groups = {}

for line in open("sets.dat"):
    line = line.split()
    if len(line) == 0:
        break
    # find the group of the first item on the row
    head = line[0]
    if head not in groups:
        group = Group(head)
        groups[head] = group
    else:
        group = groups[head]
    # for each other item on the row, merge the groups
    for node in line[1:]:
        if node not in groups:
            # its a new node, straight into the group
            group.add(node)
            groups[node] = group
        elif head not in groups[node].members:
            # merge two groups
            new_members = groups[node]
            group.union(new_members)
            for migrate in new_members.members:
                groups[migrate] = group
# list them
for k,v in groups.iteritems():
    if k == v.head:
        print v.members

Output is:

set(['T6', 'T2', 'T1'])
set(['T4', 'T5', 'T3'])