C# group by 消除重复项

发布于 2024-10-21 03:09:59 字数 874 浏览 1 评论 0原文

我正在处理一个大型兴趣点 (POI) 数据集，这些数据集都有纬度/经度值。

我想过滤掉彼此距离很近的 POI。我认为要实现这一点，我可以将纬度/经度四舍五入到小数点后的 X 位，并按结果进行分组（或调用 Distinct() 或其他方式）...

我编写了一些 LINQ 语句，其中似乎没有做我想要的事情，

 var l1 = (from p in PointsOfInterest where p.IsVisibleOnMap select p).Distinct(new EqualityComparer()).ToList();

其中 EqualityComparer 是

public class EqualityComparer : IEqualityComparer<PointOfInterest>
{
    public bool Equals(PointOfInterest x, PointOfInterest y)
    {
        return Math.Round(x.Latitude.Value, 4) == Math.Round(y.Latitude.Value, 4) && 
            Math.Round(x.Longitude.Value, 4) == Math.Round(y.Latitude.Value, 4);
    }

    public int GetHashCode(PointOfInterest obj)
    {
        return obj.GetHashCode();
    }
}

但 Equals 方法似乎永远不会被调用？！？

关于最好的方法有什么想法吗？

原文

Im working with a large dataset of point of interest (POI) which all have Lat/Long values.

I want to filter out POIs that are in close proximity to each other. I think that to achieve this I can round the Lat/Long down to X decimal places and group by the results (or call Distinct() or whatever)...

I have written a little LINQ statement which doesnt seem to do what I want,

 var l1 = (from p in PointsOfInterest where p.IsVisibleOnMap select p).Distinct(new EqualityComparer()).ToList();

where EqualityComparer is

public class EqualityComparer : IEqualityComparer<PointOfInterest>
{
    public bool Equals(PointOfInterest x, PointOfInterest y)
    {
        return Math.Round(x.Latitude.Value, 4) == Math.Round(y.Latitude.Value, 4) && 
            Math.Round(x.Longitude.Value, 4) == Math.Round(y.Latitude.Value, 4);
    }

    public int GetHashCode(PointOfInterest obj)
    {
        return obj.GetHashCode();
    }
}

but the Equals method never seems to get called?!?

Any thoughts on the best way to do this?

分享到QQ

分享到微博

如果你对这篇内容有疑问，欢迎到本站社区发帖提问参与讨论，获取更多帮助，或者扫码二维码加入 Web 技术交流群。

发布评论

需要登录才能够评论，你可以免费注册一个本站的账号。

极致的悲 2024-10-28 03:09:59

Equals() 永远不会被调用，因为 GetHashCode() 为任何两个对象返回不同的值，因为您使用的是 中定义的 GetHashCode() System.Object 类。
您需要以稍微不同的方式实现 GetHashCode()。

尝试类似的东西

public int GetHashCode(PointOfInterest obj)
{
    return obj.Longitude.Value.GetHashCode() ^ obj.Latitude.Value.GetHashCode();
}

Equals() never gets called because GetHashCode() returns different values for any two objects because you are using GetHashCode() defined in System.Object class .
You'll need to implement GetHashCode() a little differently.

try something like

public int GetHashCode(PointOfInterest obj)
{
    return obj.Longitude.Value.GetHashCode() ^ obj.Latitude.Value.GetHashCode();
}

回复收藏 0 原文

江南月 2024-10-28 03:09:59

这就是问题所在：

public int GetHashCode(PointOfInterest obj)
{
    return obj.GetHashCode();
}

您还必须适当地重写 GetHashCode()，目前可能所有项目都被视为不同，因为哈希码不匹配。

来自 MSDN 的 IEqualityComparer.GetHashCode()：

实现该方法可以提供
定制的哈希码
对象，对应于
定制平等比较
由 Equals 方法提供。

This is the problem:

public int GetHashCode(PointOfInterest obj)
{
    return obj.GetHashCode();
}

You'll have to override GetHashCode() appropriately as well, probably currently all items are considered different because the hash code doesn't match.

From MSDN for IEqualityComparer.GetHashCode():

Implement this method to provide
customized hash codes for
objects,corresponding to the
customized equality comparison
provided by the Equals method.

回复收藏 0 原文

妄断弥空 2024-10-28 03:09:59

关于执行此操作的最佳方法有什么想法吗？

简单地：

IEnumerable<PointOfInterest> result =
  from p in PointsOfInterest
  where p.IsVisibleOnMap
  group p by new
  {
    Latitude = Math.Round(p.Latitude.Value, 4),
    Longitude = Math.Round(p.Longitude.Value, 4)
  } into g
  let winner = g.First()
  select winner;

Any thoughts on the best way to do this?

Simply:

IEnumerable<PointOfInterest> result =
  from p in PointsOfInterest
  where p.IsVisibleOnMap
  group p by new
  {
    Latitude = Math.Round(p.Latitude.Value, 4),
    Longitude = Math.Round(p.Longitude.Value, 4)
  } into g
  let winner = g.First()
  select winner;

回复收藏 0 原文

~没有更多了~