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- 保存和重新加载数据集。
- Saving and reloading a dataset.

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在本视频中，我们将了解
In this video, we'll take a look

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以各种格式保存数据集
at saving a dataset in various formats

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并探索重新加载已保存数据的方法。
and explore the ways to reload the saved data.

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下载数据集时，所需的处理脚本和数据都会本地存储
When you download a dataset, the processing scripts and data

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在你的计算机上。
are stored locally on your computer.

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缓存允许 Datasets 库
The cache allows the Datasets library

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避免重新下载
to avoid re-downloading

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或每次使用时处理整个数据集。
or processing the entire dataset every time you use it.

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现在，数据以 Arrow 表的形式存储
Now, the data is stored in the form of Arrow tables

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通过访问数据集的 
whose location can be found

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cache_files 属性可以找到它的位置。
by accessing the dataset's cache_files attribute.

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在这个例子中，我们从 Hugging Face Hub 
In this example, we've downloaded the allocine dataset

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下载了 allocine 数据集，你可以看到
from the Hugging Face Hub, and you can see

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一共有三个 Arrow 文件
that there are three Arrow files

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存储在缓存中，每个文件对应一个分片数据。
stored in the cache, one for each split.

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但在很多情况下，你希望在不同的物理地址或者以不同的格式
But in many cases, you'll wanna save your dataset

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保存你的数据集。
in a different location or format.

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如表所示，Datasets 库
As shown in the table, the Datasets library

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提供了四个主要功能来实现这一点。
provides four main functions to achieve this.

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现在，你可能已经很熟悉了
Now, you're probably already familiar

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使用 CSV 和 JSON 格式，这两种格式都很棒
with the CSV and JSON formats, both of which are great

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如果你只是想快速保存一个小规模
if you just wanna quickly save a small

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或中等规模的数据集。
or medium-sized dataset.

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但是如果你的数据集很大，
But if your dataset is huge,

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你需要将其保存为 Arrow 或 Parquet 格式。
you'll wanna save it in either the Arrow or Parquet formats.

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如果你打算重新加载或在不久的将来处理数据，
Arrow files are great if you plan to reload

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Arrow 文件就很棒。
or process the data in the near future.

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虽然 Parquet 文件被设计成
While Parquet files are designed

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用于长期存储并且非常节省空间。
for long-term storage and are very space-efficient.

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让我们仔细看看每种格式。
Let's take a closer look at each format.

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保存数据集或 dataset_dict 对象
To save a dataset or a dataset_dict object

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在 Arrow 格式中，我们使用 save_to_disk 函数。
in the Arrow format, we use the save_to_disk function.

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正如你在此示例中所见，
As you can see in this example,

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只需提供我们希望将数据保存到的路径
we simply provide the path we wish to save the data to

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然后 Datasets 库
and the Datasets library

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会针对每个分片数据自动创建一个目录
will automatically create a directory

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来存储 Arrow 表和元数据。
for each split to store the Arrow table and the metadata.

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因为我们正在处理一个 dataset_dict 对象
Since we're dealing with a dataset_dict object

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其中包含多个分片数据，
that has multiple splits,

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此信息也被存储
this information is also stored

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在 dataset_dict.json 文件中。
in the dataset_dict.json file.

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现在，当想要重新加载 Arrow 数据集时，
Now, when we wanna reload the Arrow datasets,

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我们使用 load_from_disk 函数。
we use the load_from_disk function.

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只需传递数据集目录的路径，
We simply pass the path of our dataset directory,

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啊瞧，原始数据集已恢复。
and voila, the original dataset is recovered.

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如果我们想保存我们的数据集
If we wanna save our dataset

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在 CSV 格式中，我们使用 to_csv 函数。
in the CSV format, we use the to_csv function.

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在这种情况下，你需要循环
In this case, you'll need to loop

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dataset_dict 对象的分片数据
over the splits of the dataset_dict object

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并将每个数据集保存为单独的 CSV 文件。
and save each dataset as an individual CSV file.

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由于 to_csv 函数基于 Pandas 中的函数，
Since the to_csv function is based on the one from Pandas,

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你可以传递关键字参数来配置输出。
you can pass keyword arguments to configure the output.

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在这个例子中，我们将索引参数设置为 None
In this example, we've set the index argument

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以防止数据集的索引列
to None to prevent the dataset's index column

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不包含在 CSV 文件中。
from being included in the CSV files.

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要重新加载我们的 CSV 文件，
To reload our CSV files,

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就使用熟悉的 load_dataset 函数
we just then use the familiar load_dataset function

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连同 CSV 加载脚本
together with the CSV loading script

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和 data_files 参数，
and the data_files argument,

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它指定与每个分片数据关联的文件名。
which specifies the file names associated with each split.

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正如你在此示例中所见，
As you can see in this example,

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通过提供所有分片数据及其文件名，
by providing all the splits and their file names,

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我们已经恢复了原始的 dataset_dict 对象。
we've recovered the original dataset_dict object.

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现在，将数据集保存在 JSON 中
Now, to save a dataset in the JSON

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或保存为 Parquet 格式与 CSV 的情况非常相似。
or Parquet formats is very similar to the CSV case.

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我们对 JSON 文件使用 to_json 函数
We use either the to_json function for JSON files

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或 Parquet 的 to_parquet 函数。
or the to_parquet function for Parquet ones.

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就像 CSV 案例一样，我们需要遍历分片数据
And just like the CSV case, we need to loop over the splits

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将每个保存为单独的文件。
to save each one as an individual file.

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一旦我们的数据集被保存为 JSON 或 Parquet 文件，
And once our datasets are saved as JSON or Parquet files,

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我们可以重新加载它们
we can reload them again

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使用 load_dataset 函数中的合适的脚本。
with the appropriate script in the load_dataset function.

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我们只需要像以前一样提供一个 data_files 参数。
And we just need to provide a data_files argument as before.

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这个例子表明
This example shows

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我们如何以任何一种格式重新加载我们保存的数据集。
how we can reload our save datasets in either format.

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有了这个，你现在知道
And with that, you now know

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如何以各种格式保存数据集。
how to save your datasets in various formats.

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（过渡音乐）
(transition music)