104 lines
3.2 KiB
Python
104 lines
3.2 KiB
Python
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# -*- coding: utf-8 -*-
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from __future__ import print_function
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import pandas as pd
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from collections import defaultdict
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class FPNode:
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def __init__(self, item=None, count=0, parent=None):
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self.item = item
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self.count = count
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self.parent = parent
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self.children = {}
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self.next = None
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def build_fp_tree(data, min_support):
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# 构建FP树
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header_table = defaultdict(int)
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for transaction in data:
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for item in transaction:
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header_table[item] += 1
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# 移除不满足最小支持度的项
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header_table = {k: v for k, v in header_table.items() if v >= min_support}
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if not header_table:
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return None, None
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# 初始化头表
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for k in header_table:
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header_table[k] = [header_table[k], None]
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root = FPNode()
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for transaction in data:
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filtered_items = [item for item in transaction if item in header_table]
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if filtered_items:
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filtered_items.sort(key=lambda x: header_table[x][0], reverse=True)
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update_fp_tree(filtered_items, root, header_table)
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return root, header_table
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def update_fp_tree(items, node, header_table):
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# 更新FP树
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if items[0] in node.children:
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node.children[items[0]].count += 1
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else:
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new_node = FPNode(item=items[0], count=1, parent=node)
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node.children[items[0]] = new_node
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update_header_table(header_table, items[0], new_node)
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if len(items) > 1:
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update_fp_tree(items[1:], node.children[items[0]], header_table)
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def update_header_table(header_table, item, target_node):
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# 更新头表指针
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if header_table[item][1] is None:
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header_table[item][1] = target_node
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else:
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current = header_table[item][1]
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while current.next:
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current = current.next
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current.next = target_node
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def mine_fp_tree(header_table, prefix, min_support, frequent_itemsets):
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# 挖掘FP树中的频繁项集
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sorted_items = [item[0] for item in sorted(header_table.items(), key=lambda x: x[1][0])]
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for item in sorted_items:
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new_prefix = prefix.copy()
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new_prefix.add(item)
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frequent_itemsets.append(new_prefix)
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conditional_pattern_bases = find_prefix_paths(item, header_table)
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conditional_fp_tree, conditional_header_table = build_fp_tree(conditional_pattern_bases, min_support)
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if conditional_header_table:
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mine_fp_tree(conditional_header_table, new_prefix, min_support, frequent_itemsets)
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def find_prefix_paths(base_item, header_table):
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# 找到条件模式基
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paths = []
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node = header_table[base_item][1]
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while node:
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path = []
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ascend_tree(node, path)
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if path:
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paths.append(path)
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node = node.next
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return paths
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def ascend_tree(node, path):
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# 从节点向上遍历树
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while node.parent and node.parent.item:
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path.append(node.parent.item)
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node = node.parent
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def find_frequent_itemsets(data, min_support):
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# 主函数：使用FP-Growth算法挖掘频繁项集
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root, header_table = build_fp_tree(data, min_support)
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if not root:
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return []
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frequent_itemsets = []
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mine_fp_tree(header_table, set(), min_support, frequent_itemsets)
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return frequent_itemsets
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