Linq查询-如何实现数据聚合(Group Adjacent)？
Linq查询-如何实现数据聚合(Group Adjacent)？
提问于 2018-02-05 00:52:55
我有一个类Cls:
public class Cls
{
public int SequenceNumber { get; set; }
public int Value { get; set; }
}现在，让我们用以下元素填充一些集合：
Sequence
Number Value
======== =====
1 9
2 9
3 15
4 15
5 15
6 30
7 9我需要做的是，对序列号进行枚举，并检查下一个元素是否具有相同的值。如果是，则聚合值，所需输出如下：
Sequence Sequence
Number Number
From To Value
======== ======== =====
1 2 9
3 5 15
6 6 30
7 7 9如何使用LINQ查询执行此操作？
回答 2
Stack Overflow用户
发布于 2018-02-05 09:24:09
你可以用Linq的GroupBy，只有当两个项相邻时才对其进行分组，那么它很容易实现，如下所示：
var result = classes
.GroupAdjacent(c => c.Value)
.Select(g => new {
SequenceNumFrom = g.Min(c => c.SequenceNumber),
SequenceNumTo = g.Max(c => c.SequenceNumber),
Value = g.Key
});
foreach (var x in result)
Console.WriteLine("SequenceNumFrom:{0} SequenceNumTo:{1} Value:{2}", x.SequenceNumFrom, x.SequenceNumTo, x.Value);结果：
SequenceNumFrom:1 SequenceNumTo:2 Value:9
SequenceNumFrom:3 SequenceNumTo:5 Value:15
SequenceNumFrom:6 SequenceNumTo:6 Value:30
SequenceNumFrom:7 SequenceNumTo:7 Value:9这是对相邻项进行分组的扩展方法：
public static IEnumerable<IGrouping<TKey, TSource>> GroupAdjacent<TSource, TKey>(
this IEnumerable<TSource> source,
Func<TSource, TKey> keySelector)
{
TKey last = default(TKey);
bool haveLast = false;
List<TSource> list = new List<TSource>();
foreach (TSource s in source)
{
TKey k = keySelector(s);
if (haveLast)
{
if (!k.Equals(last))
{
yield return new GroupOfAdjacent<TSource, TKey>(list, last);
list = new List<TSource>();
list.Add(s);
last = k;
}
else
{
list.Add(s);
last = k;
}
}
else
{
list.Add(s);
last = k;
haveLast = true;
}
}
if (haveLast)
yield return new GroupOfAdjacent<TSource, TKey>(list, last);
}
}类如下：
public class GroupOfAdjacent<TSource, TKey> : IEnumerable<TSource>, IGrouping<TKey, TSource>
{
public TKey Key { get; set; }
private List<TSource> GroupList { get; set; }
System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator()
{
return ((System.Collections.Generic.IEnumerable<TSource>)this).GetEnumerator();
}
System.Collections.Generic.IEnumerator<TSource> System.Collections.Generic.IEnumerable<TSource>.GetEnumerator()
{
foreach (var s in GroupList)
yield return s;
}
public GroupOfAdjacent(List<TSource> source, TKey key)
{
GroupList = source;
Key = key;
}
}Stack Overflow用户
发布于 2018-02-05 10:26:48
您可以使用此Linq查询。
var values = (new[] { 9, 9, 15, 15, 15, 30, 9 }).Select((x, i) => new { x, i });
var query = from v in values
let firstNonValue = values.Where(v2 => v2.i >= v.i && v2.x != v.x).FirstOrDefault()
let grouping = firstNonValue == null ? int.MaxValue : firstNonValue.i
group v by grouping into v
select new
{
From = v.Min(y => y.i) + 1,
To = v.Max(y => y.i) + 1,
Value = v.Min(y => y.x)
};页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/-100007313
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