使用变换创建新向量 [英] Creating a new vector using a transform

问题描述

我有一个整数向量，我想将其转换为成对向量(成对包含一个 bool 和一个 int).我当前的代码很简单:

I have a vector of integers and I want to convert it to a vector of pairs (pair consists of a bool and a int). My current code is simple like this:

    std::vector<int> a;
    std::vector<std::pair<bool,int> > b;

    a.push_back(1);
    a.push_back(2);
    a.push_back(3);

    for(int i = 0; i < a.size(); ++i)
    {
        b.push_back(std::make_pair(false, a[i]));
    }

有没有什么办法可以不用自己编写循环来做到这一点?可能使用了一些算法?

Is there any way to do this without writing the loop myself? Probably using some algorithms?

推荐答案

1. 你可以创建一个函子和 std::for_each:

1. You could make a functor and std::for_each:

struct F {
    F(std::vector<std::pair<bool,int> > &b) : m_b(b){
    }

    void operator()(int x) {
        m_b.push_back(std::make_pair(false, x));
    }

    std::vector<std::pair<bool,int> > &m_b;
};

std::for_each(a.begin(), a.end(), F(b));

虽然这可能会证明比它的价值更麻烦.但至少它可以重复使用:)

Though this may prove to be more trouble than it's worth. But at least it would be reusable :).

也许 boost::bind 可以做一些事情.

Maybe there is something that could be done with boost::bind.

2. 我在想您也许可以使用带有后置插入器和转换的绑定.像这样:

2. I was thinking you might be able to use bind with a back inserter and transform. something like this:

std::transform(a.begin(), a.end(), std::back_inserter(b), boost::bind(std::make_pair<bool, int>, false, _1));

我用 std::bind1st 尝试了这个，我认为它应该可以工作，但我只能用 boost::bind 让它成功.我会继续努力...

I tried this with std::bind1st, i thought it should have worked, but i could only get it to succeed with boost::bind. I'll keep trying...

3. 这是一个非提升解决方案:

3. here's a non-boost solution:

std::transform(a.begin(), a.end(), std::back_inserter(b), std::bind1st(std::ptr_fun(std::make_pair<bool, int>), false));

4. 这是一个 C++11 解决方案(这是我目前最喜欢的):

4. here's a C++11 solution (which is my current favorite):

std::for_each(begin(a), end(a), [&b](int v) {
    b.emplace_back(false, v);
});

甚至更简单:

for(int v : a) {
    b.emplace_back(false, v);
}

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