将std :: map复制到std :: vector中 [英] Copy std::map into std::vector of pairs

问题描述

我正在尝试将地图复制到向量对中，因此可以根据向量对中的 second 数据成员对向量进行排序.我已经这样解决了:

I'm trying to copy a map into a vector of pair, so I can then sort the vector by the second data member of the pairs. I have resolved this doing like this:

void mappedWordsListSorter(){
  for (auto itr = mappedWordsList.begin(); itr != mappedWordsList.end(); ++itr){
    vectorWordsList.push_back(*itr);
  }
  sort(vectorWordsList.begin(), vectorWordsList.end(), [=](pair<string, int>& a, pair<string, int>& b){return a.second > b.second;});
}

我需要找到一种方法，而不使用原始循环，而是使用标准库.我遇到了很多仅通过传递键或映射值来执行此操作的示例.我需要复制到 pairs< string，int> 的向量中.最好的方法是什么?

I need to find a way to do this without using a raw loop, using the standard library instead. I have come across a lot of examples doing this by only transferring either the keys or the values of the map. I need to copy into a vector of pairs<string, int>. What is the best way to do it?

推荐答案

只需使用 std :: vector 的

Just use std::vector's assign member function.

//no need to call reserve, bidirectional iterators or better will compute the size and reserve internally.
vectorWordsList.assign(mappedWordsList.begin(), mappedWordsList.end());

如果向量中有您不想覆盖的现有值，请使用

If you have existing values in the vector that you don't want overwritten then use insert instead like

vectorWordsList.reserve(vectorWordsList.size() + mappedWordsList.size()); // make sure we only have a single memory allocation
vectorWordsList.insert(vectorWordsList.end(), mappedWordsList.begin(), mappedWordsList.end());

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