Question

我试图计算向量向量内的一系列元素的能量。一旦特定元素具有正确的能量，则将其推入另一矢量矢量。这是一个例子，因为很难解释：

bool energy(const std::vector<double> &vals)
{
  float sum = 0.0;
  for(unsigned i=0; (i < vals.size()); i++)
  {
     sum += (vals[i]*vals[i]);
  }
  //cout << sum << endl;
  return (sum >= 5);
}

int main(int argc, char *argv[]) {

 std::vector<vector<double> > vals {

    {0, 0, 0, 0, 0}, // This has an energy of "0" -> does not count
    {1, 1, 1, 1, 1}, // This has an energy of "5" -> push_back to vector[0]
    {1, 1, 1, 1, 1}, // This has an energy of "5" -> push_back to vector[0]
    {1, 1, 1, 1, 1}, // This has an energy of "5" -> push_back to vector[0]
    {1, 2, 1, 1, 1}, //This has an energy of "5" -> push_back to vector[0]
    {0, 0, 0, 0, 0}, // This has an energy of "0" -> does not count && start a new 
                                // vector
    {1, 2, 3, 4, 5}, // This has an energy of "55" -> push_back to vector[1]
    {1, 2, 3, 4, 5}, // This has an energy of "55" -> push_back to vector[1]
    {1, 2, 3, 4, 5}, // This has an energy of "55" -> push_back to vector[1]
    {1, 2, 3, 4, 5} // This has an energy of "55" -> push_back to vector[1]
};
std::vector<vector<double> > clusters; 
std::vector<vector<double> > tmp;

//std::for_each(vals.begin(), vals.end(), energy);

int j = 0;

for(unsigned i=0; (i < vals.size()); i++)
{
    if(energy(vals[i]))
    {
        clusters.resize(j + 1);
        clusters[j] = vals[i];
    }else if(!energy(vals[i]) && energy(vals[i+1]))
    {
        j++;
    }
}

for(unsigned i=0; (i < clusters.size()); i++)
{
    for(unsigned j=0; (j < clusters[i].size()); j++)
    {
        cout << clusters[i][j] << ' ';
    }
    cout << endl;
}
 }

应该发生什么

名为2的向量矢量应该有clusters元素，每个元素都包含以下值：

clusters[0] = { 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1 };

`clusters[1] = 1, 2, 3, 4, 5, 
      1, 2, 3, 4, 5,
      1, 2, 3, 4, 5, 
      1, 2, 3, 4, 5}`

发生了什么事？

矢量矢量似乎覆盖了插入其中的块。所以不是上面的，我只是得到它发现的最后一个元素：

`cluster[0] = {1 2 1 1 1}
cluster[1] = {1 2 3 4 5}`

我在想和尝试将每个“块”存储在包含足够能量的向量向量中，然后将所有这些值推送到vector<double>内，然后将此向量插入到块中集群..

有没有其他方法，这个问题的解决方案更简单？

Answer 1

更正后的代码：

#include<vector>
#include<iostream>
using namespace std;

bool energy(const std::vector<double> &vals)
{
  float sum = 0.0;
  for(unsigned i=0; (i < vals.size()); i++)
  {
     sum += (vals[i]*vals[i]);
  }
  //cout << sum << endl;
  return (sum >= 5);
}

int main(int argc, char *argv[]) {

 std::vector<vector<double> > vals {

    {0, 0, 0, 0, 0}, // This has an energy of "0" -> does not count
    {1, 1, 1, 1, 1}, // This has an energy of "5" -> push_back to vector[0]
    {1, 1, 1, 1, 1}, // This has an energy of "5" -> push_back to vector[0]
    {1, 1, 1, 1, 1}, // This has an energy of "5" -> push_back to vector[0]
    {1, 2, 1, 1, 1}, //This has an energy of "5" -> push_back to vector[0]
    {0, 0, 0, 0, 0}, // This has an energy of "0" -> does not count && start a new
                                // vector
    {1, 2, 3, 4, 5}, // This has an energy of "55" -> push_back to vector[1]
    {1, 2, 3, 4, 5}, // This has an energy of "55" -> push_back to vector[1]
    {1, 2, 3, 4, 5}, // This has an energy of "55" -> push_back to vector[1]
    {1, 2, 3, 4, 5} // This has an energy of "55" -> push_back to vector[1]
};
std::vector<vector<double> > tmp(vals.size());
std::vector<vector<double> > clusters(vals.size());

int j = 0;

for(unsigned i=0; (i < vals.size()); i++)
{
    if(energy(vals[i]))
    {
        clusters[j].insert(clusters[j].end(), vals[i].begin(), vals[i].end());
    }else if(!energy(vals[i]) && energy(vals[i+1]))
    {
        j++;
    }
}

for(unsigned i=0; (i < clusters.size()); i++)
{
    for(unsigned j=0; (j < clusters[i].size()); j++)
    {
        cout << clusters[i][j] << ' ';
    }
    cout << endl;
}
 }

输出结果为：

1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 2 1 1 1 
1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5

Answer 2

我更改了一段代码使其正常工作

  int j = 0;

  for(unsigned i=0; (i < vals.size()); i++)
  {
      if(energy(vals[i])) {
          clusters[j].insert(clusters[j].end, vals[i].begin(), vals[i].end());
      }
      if(!energy(vals[i]) && energy(vals[i+1])) {
        clusters.push_back( tmp );
        ++j;
      }

  }

请勿使用调整大小。您可以将空向量push_back到群集中。

对于每个附加矢量的操作，只需使用按范围插入

void insert (iterator position, InputIterator first, InputIterator last);

参考：http://en.cppreference.com/w/cpp/container/vector/insert

Answer 3

你的问题在这里：

for(unsigned i=0; (i < vals.size()); i++)
{
    if(energy(vals[i]))
    {
        clusters.resize(j + 1);
        clusters[j] = vals[i];
    }
    else if(!energy(vals[i]) && energy(vals[i+1]))
    {
        j++;
    }
}

首先，您的energy函数返回int，因此当返回值非零时，它会将条件评估为true，当它为0时，它将是false。

其次，您在push_back分支中有效地执行if，但您只是推送当前向量（您没有将其附加到现有向量）。

要解决此问题，我建议使用map<int, vector<int>>，以便您可以快速引用每个群集（例如，能量为5的群集的密钥为5，因此您可以创建一个新的向量并插入值，或附加到那里已经存在的值）。如果你需要在矢量矢量中，你可以在对它们进行排序并将它们交换到矢量矢量后迭代遍历地图。

Answer 4

你可以简化很多代码，因此阅读和理解起来会容易得多，例如你需要能量函数，你可以用算法把它写成一行：

return std::inner_product(vals.begin(), vals.end(), vals.begin(), 0.) >= 5;

将多个元素插入到2D块中

4 个答案: