Linq查询按field1分组，对field2进行计数，并根据已加入集合的值之间的计数进行筛选

本文关键字：集合 查询 筛选 之间 field1 分组 field2 Linq | 更新日期: 2023-09-27 17:49:38

我有麻烦得到我的linq查询正确。我一直拒绝使用foreach循环这样做，因为我试图更好地理解linq.

我在LinqPad中有以下数据。

void Main()
{
    var events = new[] {
        new {ID = 1, EventLevel = 1, PatientID = "1", CodeID = "2", Occurences = 0 },
        new {ID = 2, EventLevel = 2, PatientID = "1", CodeID = "2", Occurences = 0 },
        new {ID = 3, EventLevel = 1, PatientID = "2", CodeID = "1", Occurences = 0 },
        new {ID = 4, EventLevel = 3, PatientID = "2", CodeID = "2", Occurences = 0 },
        new {ID = 5, EventLevel = 1, PatientID = "3", CodeID = "3", Occurences = 0 },
        new {ID = 6, EventLevel = 3, PatientID = "1", CodeID = "4", Occurences = 0 }
    };
    var filter = new FilterCriterion();
    var searches = new List<FilterCriterion.Occurence>();
    searches.Add(new FilterCriterion.Occurence() { CodeID = "1", MinOccurences = 2, MaxOccurences = 3 });
    searches.Add(new FilterCriterion.Occurence() { CodeID = "2", MinOccurences = 2, MaxOccurences = 3 });
    filter.Searches = searches;
    var summary = from e in events
        let de = new
        {
            PatientID = e.PatientID,
            CodeID = e.CodeID
        }
        group e by de into t
        select new
        {
            PatientID = t.Key.PatientID,
                CodeID = t.Key.CodeID,
            Occurences = t.Count(d => t.Key.CodeID == d.CodeID)
        };
    var allCodes = filter.Searches.Select(i => i.CodeID);
    summary = summary.Where(e => allCodes.Contains(e.CodeID));
    // How do I find the original ID property from the "events" collection and how do I 
    // eliminate the instances where the Occurences is not between MinOccurences and MaxOccurences.
    foreach (var item in summary)
        Console.WriteLine(item);
}
public class FilterCriterion
{
   public IEnumerable<Occurence> Searches { get; set; }
   public class Occurence
   {
       public string CodeID { get; set; }
       public int? MinOccurences { get; set; }
       public int? MaxOccurences { get; set; }
   }
}

我的问题是需要通过minoccurs和maxoccurs过滤器属性过滤结果，最后我想要的"事件"对象，其中id是1,2,3和4。

如果您能提供帮助，我提前表示感谢。

Linq查询按field1分组，对field2进行计数，并根据已加入集合的值之间的计数进行筛选

要在处理结束时访问event.ID，您需要将其与第一个查询一起传递。修改select为:

// ...
group e by de into t
select new
{
    PatientID = t.Key.PatientID,
    CodeID = t.Key.CodeID,
    Occurences = t.Count(d => t.Key.CodeID == d.CodeID),
    // taking original items with us
    Items = t
};

完成后，您的最终查询(包括事件过滤器)可能像这样:

var result = summary
    // get all necessary data, including filter that matched given item
    .Select(Item => new
        {
            Item,
            Filter = searches.FirstOrDefault(f => f.CodeID == Item.CodeID)
        })
    // get rid of those without matching filter
    .Where(i => i.Filter != null)
    // this is your occurrences filtering
    .Where(i => i.Item.Occurences >= i.Filter.MinOccurences
        && i.Item.Occurences <= i.Filter.MaxOccurences)
    // and finally extract original events IDs
    .SelectMany(i => i.Item.Items)
    .Select(i => i.ID);

生成1, 2。3和4被忽略了，因为它们没有得到过去发生的过滤。

我已经在linqpad上运行了你的程序。

我的理解是你想用过滤器来过滤。minoccurs和过滤器。maxoccurs on results data set.

可以使用Where子句添加额外的过滤器。

if (filter.MinOccurences.HasValue)
 summary = summary.Where (x=> x.Occurences >= filter.MinOccurences);
if (filter.MaxOccurences.HasValue)
 summary = summary.Where (x=> x.Occurences <= filter.MaxOccurences);
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