UnionBin Linq实施 [英] UnionBy Linq Implementation
问题描述
我需要在Union上实现一个比较对象属性(而不是对象本身)的实现.我提出了以下建议:
public static IEnumerable<TSource> UnionBy<TSource, TKey>(
this IEnumerable<TSource> first,
IEnumerable<TSource> second,
Func<TSource, TKey> keySelector,
IEqualityComparer<TKey> keyComparer = null)
{
HashSet<TKey> keys = new HashSet<TKey>(keyComparer);
foreach (TSource element in first)
{
if (keys.Add(keySelector(element)))
{
yield return element;
}
}
foreach (TSource element in second)
{
if (!keys.Add(keySelector(element)))
{
continue;
}
yield return element;
}
}
我可以这样说:
result = first.UnionBy(second, x => x.Property1);
这对我有用,但是我想知道Linq中是否还没有实现我缺少的东西(除了实现我自己的EqualityComparer 外,对我来说似乎不太直观).>
因为我每次想要这个联合时都不会使用相同的属性,所以我要么必须为每种情况创建多个EqualityComparer
,但这对我来说似乎不正确,或者是制作一些通用的EqualityComparer
这将包含一个属性选择器Func.对我来说,似乎不像提供一个接受属性选择器本身的通用Linq扩展那样直观.
是的,您可以按如下所示编写它:
var q = first.Concat(second).GroupBy(x => x.Property1).Select(x => x.First());
I needed an implementation on Union that compares a property of an object, rather the objects themselves. I came up with the following:
public static IEnumerable<TSource> UnionBy<TSource, TKey>(
this IEnumerable<TSource> first,
IEnumerable<TSource> second,
Func<TSource, TKey> keySelector,
IEqualityComparer<TKey> keyComparer = null)
{
HashSet<TKey> keys = new HashSet<TKey>(keyComparer);
foreach (TSource element in first)
{
if (keys.Add(keySelector(element)))
{
yield return element;
}
}
foreach (TSource element in second)
{
if (!keys.Add(keySelector(element)))
{
continue;
}
yield return element;
}
}
which I can use by saying something along the lines of:
result = first.UnionBy(second, x => x.Property1);
Which works for me, but I was wondering if there wasn't something already implemented in Linq that I was missing (other than implementing my own EqualityComparer which to me seems less intuitive).
Since I won't be using the same properties every time I want this union I would either have to make multiple EqualityComparer
's for each situation which doesn't seem correct to me, or make some generic EqualityComparer
that would take in a property selector Func. It seemed less intuitive to me than just providing a generic Linq extension that accepted the property selector itself.
Yes you can write it as follows instead:
var q = first.Concat(second).GroupBy(x => x.Property1).Select(x => x.First());
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