List To Group 映射仅可用于列表，它通过仅保留列表的第一个项目将列表转化成一个组。

The List To Group projection can only be used for lists, and it turns the list into a group by retaining only the first item of the list.

youdao

不过，与filter不同的是，map通常保留列表的每个元素，使用对每个值应用代码得到的结果替换这些值。

But, unlike filter , a map always keeps every element of a list, replacing each value with the result of evaluating the code on that value.

youdao

由于与本讨论不相关的许多理由，需要保留该列表并以那种格式加以维护，以在可以预见的未来使用。

For many reasons that are irrelevant to this discussion, the list will remain and be maintained in that format for the foreseeable future.

youdao