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（空气呼啸）
(air whooshing)

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- 你是在正确的地方
- You are at the right place

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如果你想了解什么是字节对编码(BPE)算法
if you want to understand what the Byte Pair Encoding

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子词分词化算法是，
subword tokenization algorithm is,

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如何训练它
how to train it

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以及文本的分词化是如何完成的
and how the tokenization of a text is done

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用这个算法。
with this algorithm.

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BPE 算法
The BPE algorithm

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最初被提出作为文本压缩算法
was initially proposed as a text compression algorithm

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但它也非常适合
but it is also very well suited

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作为你的语言模型的分词器。
as a tokenizer for your language models.

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BPE 的思想是分词
The idea of BPE is to divide words

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进入一系列 “子词单元”
into a sequence of'subword units'

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其是参考语料库中频繁出现的单位
which are units that appear frequently in a reference corpus

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也是我们用来训练它的语料库。
which is, the corpus we used to train it.

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BPE 分词器是如何训练的？
How is a BPE tokenizer trained?

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首先，我们必须得到一个文本语料库。
First of all, we have to get a corpus of texts.

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我们不会在这个原始文本上训练我们的分词器
We will not train our tokenizer on this raw text

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但我们首先将其规范化
but we will first normalize it

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然后对其进行预标记。
then pre-tokenize it.

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作为预标记化
As the pre-tokenization

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将文本分成单词列表，
divides the text into a list of words,

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我们可以用另一种方式表示我们的语料库
we can represent our corpus in another way

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通过收集相同的词
by gathering together the same words

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并通过维护一个柜，
and by maintaining a counter,

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这里用蓝色表示。
here represented in blue.

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要了解训练的工作原理，
To understand how the training works,

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我们认为这个小语料库由以下单词组成：
we consider this toy corpus composed of the following words:

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huggingface, hugging, hug, hugger, 等
huggingface, hugging, hug, hugger, etc.

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BPE 是一种从初始词汇表开始的算法
BPE is an algorithm that starts with an initial vocabulary

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然后将其增加到所需的大小。
and then increases it to the desired size.

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为了建立初始词汇表，
To build the initial vocabulary,

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我们从分离语料库的每个词开始
we start by separating each word of the corpus

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组成它们的基本单元列表，
into a list of elementary units that compose them,

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在这里, 字符。
here, the characters.

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我们在词汇表中列出所有出现的字符
We list in our vocabulary all the characters that appear

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这将构成我们最初的词汇表。
and that will constitute our initial vocabulary.

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现在让我们看看如何增加它。
Let's now see how to increase it.

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我们回到我们拆分的语料库，
We return to our split corpus,

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我们将逐字逐句
we will go through the words one by one

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并计算 token 对的所有出现次数。
and count all the occurrences of token pairs.

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第一对由标记 “h” 和 “u” 组成，
The first pair is composed of the token 'h' and 'u',

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第二个 "u" 和 "g"，
the second 'u' and 'g',

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我们继续这样，直到我们有完整的列表。
and we continue like that until we have the complete list.

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一旦我们知道所有的对
Once we know all the pairs

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以及它们出现的频率，
and their frequency of appearance,

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我们将选择出现频率最高的那个。
we will choose the one that appears the most frequently.

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这是由字母 “l” 和 “e” 组成的一对。
Here it is the pair composed of the letters 'l' and 'e'.

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我们注意到我们的第一个合并规则
We note our first merging rule

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然后我们将新 token 添加到我们的词汇表中。
and we add the new token to our vocabulary.

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然后我们可以将此合并规则应用于我们的拆分。
We can then apply this merging rule to our splits.

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你可以看到我们已经合并了所有的 token 对
You can see that we have merged all the pairs of tokens

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由标记 “l” 和 “e” 组成。
composed of the tokens 'l' and 'e'.

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现在，我们只需要重现相同的步骤
And now, we just have to reproduce the same steps

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与我们的新拆分。
with our new splits.

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我们计算出现频率
We calculate the frequency of occurrence

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对每对 token ，
of each pair of tokens,

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我们选择频率最高的一对，
we select the pair with the highest frequency,

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我们在我们的合并规则中注意到它，
we note it in our merge rules,

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我们将新的 token 添加到词汇表中
we add the new one token the vocabulary

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然后我们合并所有的 token 对
and then we merge all the pairs of tokens

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由标记 “le” 和 “a” 组成，进入我们的拆分。
composed of the token 'le' and 'a' into our splits.

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我们可以重复这个操作
And we can repeat this operation

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直到我们达到所需的词汇量。
until we reach the desired vocabulary size.

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在这里，当我们的词汇量达到 21 个 token 时，我们就停止了。
Here, we stopped when our vocabulary reached 21 tokens.

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我们现在可以看到，比起训练开始时 
We can see now that the words of our corpus

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我们的语料库中的单词
are now divided into far fewer tokens

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被分成了更少的 token
than at the beginning of the training.

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而我们的算法
And that our algorithm

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学会了部首 “hug” 和 “learn”
has learned the radicals 'hug' and 'learn'

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以及动词结尾 “ing”。
and also the verbal ending 'ing'.

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现在我们已经学会了我们的词汇
Now that we have learned our vocabulary

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和合并规则，我们可以标记新文本。
and merging rules, we can tokenize new texts.

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例如，
For example,

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如果我们想标记 “hugs” 这个词，
if we want to tokenize the word 'hugs',

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首先我们将它分成基本单元
first we'll divide it into elementary units

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所以它变成了一个字符序列。
so it became a sequence of characters.

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然后，我们将通过我们的合并规则
Then, we'll go through our merge rules

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直到我们有一个我们可以应用。
until we have one we can apply.

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在这里，我们可以合并字母 “h” 和 “u”。
Here, we can merge the letters 'h' and 'u'.

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在这里，我们可以合并 2 个 token 以获得新 token “hug”。
And here, we can merge 2 tokens to get the new token 'hug'.

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当我们到达合并规则的末尾时，
When we get to the end of our merge rules,

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分词化完成。
the tokenization is finished.

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就是这样。
And that's it.

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我希望现在的 BPE 算法
I hope that now the BPE algorithm

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对你而言不再是秘密！
has no more secret for you!

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（空气呼啸）
(air whooshing)

