C ++排序和跟踪索引 [英] C++ sorting and keeping track of indexes

问题描述

使用C ++，希望是标准库，我想按升序对一系列样本进行排序，但我也想记住新样本的原始索引。

Using C++, and hopefully the standard library, I want to sort a sequence of samples in ascending order, but I also want to remember the original indexes of the newly samples.

例如，我有一个样本的集合或向量或矩阵 A：[5，2，1，4，3] 。我想把这些排序为 B：[1,2,3,4,5] ，但我也想记住值的原始索引，所以我可以得到另一个集合，其将是：
C：[2,1,4,3,0] - 其对应于'B中的每个元素的索引

For example, I have a set, or vector, or matrix of samples A : [5, 2, 1, 4, 3]. I want to sort these to be B : [1,2,3,4,5], but I also want to remember the original indexes of the values, so I can get another set which would be: C : [2, 1, 4, 3, 0 ] - which corresponds to the index of the each element in 'B', in the original 'A'.

例如，在Matlab中，您可以：

For example, in Matlab you can do:

 [a,b]=sort([5, 8, 7])
 a = 5 7 8
 b = 1 3 2

任何人都可以看到一个好的方法来做这个？

Can anyone see a good way to do this?

推荐答案

使用C ++ 11 lambdas

Using C++11 lambdas

template <typename T>
vector<size_t> sort_indexes(const vector<T> &v) {

  // initialize original index locations
  vector<size_t> idx(v.size());
  iota(idx.begin(), idx.end(), 0);

  // sort indexes based on comparing values in v
  sort(idx.begin(), idx.end(),
       [&v](size_t i1, size_t i2) {return v[i1] < v[i2];});

  return idx;
}

现在，您可以在迭代中使用返回的索引向量，例如

Now you can use the returned index vector in iterations such as

for (auto i: sort_indexes(v)) {
  cout << v[i] << endl;
}

显然，你也可以选择提供自己的原始索引向量， ，比较器或使用额外向量在sort_indexes函数中自动重新排序v。

Obviously, you can also choose to supply your own original index vector, sort function, comparator, or automatically reorder v in the sort_indexes function using an extra vector.

这篇关于C ++排序和跟踪索引的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！