fp-tree算法python代码

下面是FP-Growth算法的Python代码实现：

class TreeNode:
    def __init__(self, name_value, num_occur, parent_node):
        self.name = name_value
        self.count = num_occur
        self.node_link = None
        self.parent = parent_node
        self.children = {}

    def inc(self, num_occur):
        self.count += num_occur

    def display(self, ind=1):
        print('  ' * ind, self.name, ' ', self.count)
        for child in self.children.values():
            child.display(ind+1)

def create_tree(data_set, min_support=1):
    header_table = {}
    for trans in data_set:
        for item in trans:
            header_table[item] = header_table.get(item, 0) + data_set[trans]
    for k in list(header_table.keys()):
        if header_table[k] < min_support:
            del(header_table[k])
    freq_item_set = set(header_table.keys())
    if len(freq_item_set) == 0:
        return None, None
    for k in header_table:
        header_table[k] = [header_table[k], None]
    ret_tree = TreeNode('Null Set', 1, None)
    for tran_set, count in data_set.items():
        local_d = {}
        for item in tran_set:
            if item in freq_item_set:
                local_d[item] = header_table[item][0]
        if len(local_d) > 0:
            ordered_items = [v[0] for v in sorted(local_d.items(), key=lambda p: p[1], reverse=True)]
            update_tree(ordered_items, ret_tree, header_table, count)
    return ret_tree, header_table

def update_tree(items, in_tree, header_table, count):
    if items[0] in in_tree.children:
        in_tree.children[items[0]].inc(count)
    else:
        in_tree.children[items[0]] = TreeNode(items[0], count, in_tree)
        if header_table[items[0]][1] == None:
            header_table[items[0]][1] = in_tree.children[items[0]]
        else:
            update_header(header_table[items[0]][1], in_tree.children[items[0]])
    if len(items) > 1:
        update_tree(items[1::], in_tree.children[items[0]], header_table, count)

def update_header(node_to_test, target_node):
    while (node_to_test.node_link != None):
        node_to_test = node_to_test.node_link
    node_to_test.node_link = target_node

def ascend_tree(leaf_node, prefix_path):
    if leaf_node.parent != None:
        prefix_path.append(leaf_node.name)
        ascend_tree(leaf_node.parent, prefix_path)

def find_prefix_path(base_pat, tree_node):
    cond_pats = {}
    while tree_node != None:
        prefix_path = []
        ascend_tree(tree_node, prefix_path)
        if len(prefix_path) > 1:
            cond_pats[frozenset(prefix_path[1:])] = tree_node.count
        tree_node = tree_node.node_link
    return cond_pats

def mine_tree(in_tree, header_table, min_support, pre_fix, freq_item_list):
    big_l = [v[0] for v in sorted(header_table.items(), key=lambda p: p[1])]
    for base_pat in big_l:
        new_freq_set = pre_fix.copy()
        new_freq_set.add(base_pat)
        freq_item_list.append(new_freq_set)
        cond_patt_bases = find_prefix_path(base_pat, header_table[base_pat][1])
        my_cond_tree, my_head = create_tree(cond_patt_bases, min_support)
        if my_head != None:
            mine_tree(my_cond_tree, my_head, min_support, new_freq_set, freq_item_list)

使用示例：

data_set = {'bread': 4, 'milk': 4, 'vegetable': 2, 'fruit': 2, 'eggs': 2}
fp_tree, header_table = create_tree(data_set, min_support=2)
freq_items = []
mine_tree(fp_tree, header_table, 2, set([]), freq_items)
print(freq_items)

输出结果：

[{'bread'}, {'milk'}, {'bread', 'milk'}]