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{
"cells": [
{
"cell_type": "markdown",
"metadata": {},
"source": [
"## 搭建一个分词工具\n",
"\n",
"### Part 1 基于枚举方法来搭建中文分词工具\n",
"\n",
"此项目需要的数据：\n",
"1. 综合类中文词库.xlsx： 包含了中文词，当做词典来用\n",
"2. 以变量的方式提供了部分unigram概率 word_prob\n",
"\n",
"\n",
"举个例子： 给定词典=[我们 学习 人工 智能 人工智能 未来 是]， 另外我们给定unigram概率：p(我们)=0.25, p(学习)=0.15, p(人工)=0.05, p(智能)=0.1, p(人工智能)=0.2, p(未来)=0.1, p(是)=0.15\n",
"\n",
"#### Step 1: 对于给定字符串：”我们学习人工智能，人工智能是未来“, 找出所有可能的分割方式\n",
"- [我们，学习，人工智能，人工智能，是，未来]\n",
"- [我们，学习，人工，智能，人工智能，是，未来]\n",
"- [我们，学习，人工，智能，人工，智能，是，未来]\n",
"- [我们，学习，人工智能，人工，智能，是，未来]\n",
".......\n",
"\n",
"\n",
"#### Step 2: 我们也可以计算出每一个切分之后句子的概率\n",
"- p(我们，学习，人工智能，人工智能，是，未来)= -log p(我们)-log p(学习)-log p(人工智能)-log p(人工智能)-log p(是)-log p(未来)\n",
"- p(我们，学习，人工，智能，人工智能，是，未来)=-log p(我们)-log p(学习)-log p(人工)-log p(智能)-log p(人工智能)-log p(是)-log p(未来)\n",
"- p(我们，学习，人工，智能，人工，智能，是，未来)=-log p(我们)-log p(学习)-log p(人工)-log p(智能)-log p(人工)-log p(智能)-log p(是)-log p(未来)\n",
"- p(我们，学习，人工智能，人工，智能，是，未来)=-log p(我们)-log p(学习)-log p(人工智能)-log p(人工)-log p(智能)-log(是)-log p(未来)\n",
".....\n",
"\n",
"#### Step 3: 返回第二步中概率最大的结果"
]
},
{
"cell_type": "code",
"execution_count": 1,
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"词典长度: 298032\n",
"1.0000000000000002\n"
]
}
],
"source": [
"# TODO: 第一步： 从综合类中文词库.xlsx 中读取所有中文词。\n",
"# hint: 思考一下用什么数据结构来存储这个词典会比较好？ 要考虑我们每次查询一个单词的效率。 \n",
"\n",
"import pandas as pd\n",
"from collections import defaultdict\n",
"\n",
"df = pd.read_excel('综合类中文词库.xlsx', header=None)\n",
"\n",
"dic_words = defaultdict(int)\n",
"for i in df[0].tolist():\n",
" dic_words[i] += 1 # 保存词典库中读取的单词\n",
"print(f'词典长度: {len(dic_words)}')\n",
"\n",
"# 以下是每一个单词出现的概率。为了问题的简化，我们只列出了一小部分单词的概率。 在这里没有出现的的单词但是出现在词典里的，统一把概率设置成为0.00001\n",
"# 比如 p(\"学院\")=p(\"概率\")=...0.00001\n",
"\n",
"word_prob = {\"北京\":0.03,\"的\":0.08,\"天\":0.005,\"气\":0.005,\"天气\":0.06,\"真\":0.04,\"好\":0.05,\"真好\":0.04,\"啊\":0.01,\"真好啊\":0.02, \n",
" \"今\":0.01,\"今天\":0.07,\"课程\":0.06,\"内容\":0.06,\"有\":0.05,\"很\":0.03,\"很有\":0.04,\"意思\":0.06,\"有意思\":0.005,\"课\":0.01,\n",
" \"程\":0.005,\"经常\":0.08,\"意见\":0.08,\"意\":0.01,\"见\":0.005,\"有意见\":0.02,\"分歧\":0.04,\"分\":0.02, \"歧\":0.005}\n",
"\n",
"print (sum(word_prob.values()))"
]
},
{
"cell_type": "code",
"execution_count": 2,
"metadata": {},
"outputs": [],
"source": [
"def word_break(s, dic):\n",
" def sentences(cur):\n",
" result = []\n",
" if cur < len(s):\n",
" for next in range(cur + 1, len(s) + 1):\n",
" if s[cur:next] in dic: #列表切片是前闭后开的过程\n",
" result = result + [s[cur:next] + (tail and ',' + tail) for tail in sentences(next)]\n",
" else:\n",
" return ['']\n",
" return result\n",
"\n",
" list_new = []\n",
" for line in sentences(0):\n",
" line = line.split(\",\")\n",
" list_new.append(line)\n",
" return list_new"
]
},
{
"cell_type": "code",
"execution_count": 3,
"metadata": {},
"outputs": [],
"source": [
"import math\n",
"def get_best_segments(segments):\n",
" scores = []\n",
" for segment in segments:\n",
" score = 0\n",
" for word in segment:\n",
" prob = word_prob[word] if word in word_prob else 0.00001\n",
" score -= math.log(prob)\n",
" scores.append(score)\n",
" index = scores.index(min(scores))\n",
" return segments[index]"
]
},
{
"cell_type": "code",
"execution_count": 4,
"metadata": {},
"outputs": [],
"source": [
"## TODO 请编写word_segment_naive函数来实现对输入字符串的分词\n",
"def word_segment_naive(input_str):\n",
" \"\"\"\n",
" 1. 对于输入字符串做分词，并返回所有可行的分词之后的结果。\n",
" 2. 针对于每一个返回结果，计算句子的概率\n",
" 3. 返回概率最高的最作为最后结果\n",
" \n",
" input_str: 输入字符串 输入格式：“今天天气好”\n",
" best_segment: 最好的分词结果 输出格式：[\"今天\"，\"天气\"，\"好\"]\n",
" \"\"\"\n",
"\n",
" # TODO： 第一步： 计算所有可能的分词结果，要保证每个分完的词存在于词典里，这个结果有可能会非常多。 \n",
" segments = word_break(input_str, dic_words) # 存储所有分词的结果。如果次字符串不可能被完全切分，则返回空列表(list)\n",
" # 格式为：segments = [[\"今天\"，“天气”，“好”],[\"今天\"，“天“，”气”，“好”],[\"今“，”天\"，“天气”，“好”],...]\n",
" \n",
" # TODO: 第二步：循环所有的分词结果，并计算出概率最高(?)的分词结果，并返回\n",
" best_segment = get_best_segments(segments)\n",
" return best_segment "
]
},
{
"cell_type": "code",
"execution_count": 5,
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"['北京', '的', '天气', '真好', '啊']\n",
"['今天', '的', '课程', '内容', '很', '有意思']\n",
"['经常', '有', '意见', '分歧']\n"
]
}
],
"source": [
"# 测试\n",
"print (word_segment_naive(\"北京的天气真好啊\"))\n",
"print (word_segment_naive(\"今天的课程内容很有意思\"))\n",
"print (word_segment_naive(\"经常有意见分歧\"))"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"### Part 2 基于维特比算法来优化上述流程\n",
"\n",
"此项目需要的数据：\n",
"1. 综合类中文词库.xlsx： 包含了中文词，当做词典来用\n",
"2. 以变量的方式提供了部分unigram概率word_prob\n",
"\n",
"\n",
"举个例子： 给定词典=[我们 学习 人工 智能 人工智能 未来 是]， 另外我们给定unigram概率：p(我们)=0.25, p(学习)=0.15, p(人工)=0.05, p(智能)=0.1, p(人工智能)=0.2, p(未来)=0.1, p(是)=0.15\n",
"\n",
"#### Step 1: 根据词典，输入的句子和 word_prob来创建带权重的有向图（Directed Graph） 参考：课程内容\n",
"有向图的每一条边是一个单词的概率（只要存在于词典里的都可以作为一个合法的单词），这些概率已经给出（存放在word_prob）。\n",
"注意：思考用什么方式来存储这种有向图比较合适？ 不一定只有一种方式来存储这种结构。 \n",
"\n",
"#### Step 2: 编写维特比算法（viterebi）算法来找出其中最好的PATH， 也就是最好的句子切分\n",
"具体算法参考课程中讲过的内容\n",
"\n",
"#### Step 3: 返回结果\n",
"跟PART 1的要求一致"
]
},
{
"cell_type": "code",
"execution_count": 6,
"metadata": {},
"outputs": [],
"source": [
"def DAG(sentence):\n",
" DAG = {} #DAG空字典，用来构建DAG有向无环图\n",
" N = len(sentence)\n",
" for k in range(N):\n",
" tmplist = [] \n",
" i = k\n",
" frag = sentence[k]\n",
" while i < N:\n",
" if frag in word_prob:\n",
" tmplist.append(i) \n",
" i += 1 \n",
" frag = sentence[k:i + 1] \n",
" if not tmplist:\n",
" tmplist.append(k)\n",
" DAG[k] = tmplist\n",
" return DAG"
]
},
{
"cell_type": "code",
"execution_count": 7,
"metadata": {},
"outputs": [],
"source": [
"## TODO 请编写word_segment_viterbi函数来实现对输入字符串的分词\n",
"def word_segment_viterbi(input_str):\n",
" \"\"\"\n",
" 1. 基于输入字符串，词典，以及给定的unigram概率来创建DAG(有向图）。\n",
" 2. 编写维特比算法来寻找最优的PATH\n",
" 3. 返回分词结果\n",
" \n",
" input_str: 输入字符串 输入格式：“今天天气好”\n",
" best_segment: 最好的分词结果 输出格式：[\"今天\"，\"天气\"，\"好\"]\n",
" \"\"\"\n",
" \n",
" # TODO: 第一步：根据词典，输入的句子，以及给定的unigram概率来创建带权重的有向图（Directed Graph） 参考：课程内容\n",
" # 有向图的每一条边是一个单词的概率（只要存在于词典里的都可以作为一个合法的单词），这些概率在 word_prob，如果不在word_prob里的单词但在\n",
" # 词典里存在的，统一用概率值0.00001。\n",
" # 注意：思考用什么方式来存储这种有向图比较合适？ 不一定有只有一种方式来存储这种结构。 \n",
" N=len(sentence)\n",
" graph = DAG(sentence)\n",
" \n",
" # TODO： 第二步： 利用维特比算法来找出最好的PATH， 这个PATH是P(sentence)最大或者 -log P(sentence)最小的PATH。\n",
" # hint: 思考为什么不用相乘: p(w1)p(w2)...而是使用negative log sum: -log(w1)-log(w2)-...\n",
" route={}\n",
" route[N] = (0, 0)\n",
" \n",
" for idx in range(N - 1, -1, -1):\n",
" distance = (((word_prob.get(sentence[idx:x + 1]) or 0) + route[x + 1][0], x) for x in dag[idx])\n",
" route[idx] = max(distance)\n",
" \n",
" # TODO: 第三步： 根据最好的PATH, 返回最好的切分\n",
" x = 0\n",
" best_segment = []\n",
" while x < N:\n",
" y = route[x][1] + 1\n",
" word = sentence[x:y]\n",
" best_segment.append(word)\n",
" x = y\n",
"\n",
" return best_segment "
]
},
{
"cell_type": "code",
"execution_count": 8,
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"['北京', '的', '天气', '真好', '啊']\n",
"['今天', '的', '课程', '内容', '很', '有意思']\n",
"['经常', '有', '意见', '分歧']\n"
]
}
],
"source": [
"# 测试\n",
"print (word_segment_naive(\"北京的天气真好啊\"))\n",
"print (word_segment_naive(\"今天的课程内容很有意思\"))\n",
"print (word_segment_naive(\"经常有意见分歧\"))"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"# TODO: 第一种方法和第二种方法的时间复杂度和空间复杂度分别是多少？\n",
"第一个方法： \n",
"时间复杂度= , 空间复杂度=\n",
"\n",
"第二个方法：\n",
"时间复杂度= , 空间复杂度="
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"# TODO：如果把上述的分词工具持续优化，有哪些可以考虑的方法？ （至少列出3点）\n",
"- 0. （例）， 目前的概率是不完整的，可以考虑大量的语料库，然后从中计算出每一个词出现的概率，这样更加真实\n",
"- 1.\n",
"- 2.\n",
"- 3. "
]
},
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