一个视频：https://www.bilibili.com/video/BV1mb4y1y7EB/?spm_id_from=333.337.search-card.all.click&vd_source=7a1a0bc74158c6993c7355c5490fc600
这里有个视频，讲解得更加生动形象一些
总得来说，词袋模型(Bow, bag-of-words) 是最简单的 “文本 —> 矢量”(把文本转为矢量) 模型
二元分类和多元分类的两个例子放在末尾
以下是 Claude3 的解释，我们慢慢看
The bag-of-words model is a simplifying representation used in natural language processing (NLP). In this representation, a text (such as a sentence or a document) is represented as an unordered collection of words, disregarding grammar and word order.
bag-of-words 模型是 NLP领域 里的一个简化表示方法。在这种表示方法里，一个文本(比如一个句子或者是一个文档) 会被表示成一个乱序的单词集合，无视里面的语法和单词顺序。
Here’s how it works:
- A vocabulary of known words is created from the corpus of texts.
- Each text is represented as a vector, with one dimension for each word in the vocabulary.
- If a word appears in the text, its value in the vector is non-zero (typically 1 or a number representing frequency); otherwise, it is zero.
For example, if the vocabulary is [“hello”, “goodbye”, “computer”], then the sentence “hello hello computer” would be represented by the vector [2, 0, 1].
如下，是 bag-of-words 的工作方法：
- 一堆已知单词的词汇表是从语料库里创建出来的
- 每一个文本都可以使用一个向量表示，词汇表中的每一个单词都可以使用一个一维向量来表示
- 如果一个单词在文本中出现，它在矢量中的值是 non-zero，否则就是 0。
举个例子，如果词汇表是 [“hello”, “goodbye”, “computer”]，那么这句 “hello hello computer” 就可以用矢量 [2, 0, 1] 表示
The advantages of this model are its simplicity and the fact that it allows for straightforward application of techniques from fields like machine learning and information retrieval.
However, the bag-of-words model has several shortcomings:
- It disregards word order and grammar, which can be very important in natural language.
- It assumes that all words are equally important, ignoring semantics.
- For large vocabularies, the resulting vector can be very high-dimensional and sparse.
Despite these limitations, the bag-of-words model can serve as a baseline for more advanced NLP techniques and may still have some uses in simple applications.
这个模型的优点是：很简单，并且它允许直接应用来自机器学习和信息检索等领域的技术。
然而，bag-of-words 模型也有几个缺点：
- 它忽略了单词的顺序和语法结构,而这在自然语言中是非常重要的。 （单词向量无法展示单词顺序和语法结构）
- 它假设所有单词同等重要,忽视了词义语义信息。 （假设所有单词同等重要）
- 对于大型词汇表,生成的向量往往是非常高维且稀疏的。 （大型词汇表中，向量高维且稀疏）
尽管有这些限制，bag-of-words 模型仍然可以作为一些先进的 NLP技术的 baseline，并且在一些简单的应用中都是有用例的
In modern NLP systems, more advanced techniques like word embeddings (e.g., Word2Vec, GloVe, BERT) are commonly used to capture richer semantic and syntactic information.
在现代NLP系统中,通常采用更先进的技术,如词嵌入(例如Word2Vec、GloVe、BERT)来捕获更丰富的语义和语法信息。
二元分类和多元分类的两个例子放在末尾
二元分类：
多元分类：
