I want to sort a class that contains vector type.

For example, 

```
class Line
{
public;
vector<float> Angle;
vector<float> Length;
}

```

The angle and length are the line segment's angle and length.

```
Line LineSegment;
LineSegment.Angle.push_back(10.0);   LineSegment.Length.push_back(100.0);
LineSegment.Angle.push_back(20.0);   LineSegment.Length.push_back(50.0);
LineSegment.Angle.push_back(30.0);   LineSegment.Length.push_back(10.0);

```

First line segment has angle of 10 degree and length of 100 pixels.
Second : 20 degree, 50 pixels, third : 30 degree, 10 pixels.

For this example, I'd like to sort by length, so that
the result should have reverse index of original.

How can I do this? I searched several sorting algorithms, however they solved sorting of vectors or classes, or vector that contains class type.