The function in Listing 20 returns a vector of vectors. This is because each document could generate zero to many map entries, and each map entry is represented as a vector.

清单20中的函数返回矢量的矢量，这是因为每个文档都可能生成零到多个映射条目，而每个映射条目都被表示为一个矢量。

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The function in Listing 20 returns a vector of vectors. This is because each document could generate zero to many map entries, and each map entry is represented as a vector.

清单20中的函数返回矢量的矢量，这是因为每个文档都可能生成零到多个映射条目，而每个映射条目都被表示为一个矢量。

youdao