Question

我有一个Linq 查询

var x = (from t in types select t).GroupBy(g =>g.Type)

将对象按其类型分组,结果我要有包含所有组合对象及其计数的单一新对象。类似 :

type1, 30    
type2, 43    
type3, 72

更清晰:组合结果应归在一个对象中,而不是每个项目类型的对象

Answer 1

读取:101 LINQ 样本 ,该样本 < a href='"http://code.msdn.microsoft.com/LINQ-to-DataSets-grouping-c62703ea' rel=“无随从 noreferr'>LINQ -群集操作员 ,来自微软MSDN网站

var x = from t in types  group t by t.Type
         into grp    
         select new { type = grp.key, count = grp.Count() };

对于单个对象,请使用 StringBuilder 并附加,或将其转换为字典形式:

    // fordictionary 
  var x = (from t in types  group t by t.Type
     into grp    
     select new { type = grp.key, count = grp.Count() })
   .ToDictionary( t => t.type, t => t.count); 

   //for stringbuilder not sure for this 
  var x = from t in types  group t by t.Type
         into grp    
         select new { type = grp.key, count = grp.Count() };
  StringBuilder MyStringBuilder = new StringBuilder();

  foreach (var res in x)
  {
       //: is separator between to object
       MyStringBuilder.Append(result.Type +" , "+ result.Count + " : ");
  }
  Console.WriteLine(MyStringBuilder.ToString());

Answer 2

但2016年, 我写了以下LINQ:

List<ObjectType> objectList = similarTypeList.Select(o =>
    new ObjectType
    {
        PropertyOne = o.PropertyOne,
        PropertyTwo = o.PropertyTwo,
        PropertyThree = o.PropertyThree
    }).ToList();

Answer 3

组合的所有 对象 或所有 类型 ? 听起来你可能想要 :

var query = types.GroupBy(t => t.Type)
                 .Select(g => new { Type = g.Key, Count = g.Count() });

foreach (var result in query)
{
    Console.WriteLine("{0}, {1}", result.Type, result.Count);
}

如果您在字典中想要 , 您可以只使用 :

var query = types.GroupBy(t => t.Type)
                 .ToDictionary(g => g.Key, g => g.Count());

不需要选择成对,而然后构建字典。

Answer 4

var x = from t in types
        group t by t.Type into grouped
        select new { type = grouped.Key,
                     count = grouped.Count() };

Answer 5

如果您想要对每种类型进行搜索以获得频率,您就需要将查点转换成字典。

var types = new[] {typeof(string), typeof(string), typeof(int)};
var x = types
        .GroupBy(type => type)
        .ToDictionary(g => g.Key, g => g.Count());
foreach (var kvp in x) {
    Console.WriteLine("Type {0}, Count {1}", kvp.Key, kvp.Value);
}
Console.WriteLine("string has a count of {0}", x[typeof(string)]);

Answer 6

这是用于从 LINQ 查询中创建新对象所需的语法的伟大文章。

但是,如果在对象字段中填充任务比简单的任务要简单得多,例如,将字符串对整数进行剖析,而其中一项失败,则无法调试这一点。在任何单个任务上无法创建断点。

如果您将所有任务移到子例程, 从那里返回一个新的对象, 并试图在常规中设置断点, 您可以在常规中设置断点, 但断点永远不会被触发。

而不是:

var query2 = from c in doc.Descendants("SuggestionItem")
                select new SuggestionItem
                       { Phrase = c.Element("Phrase").Value
                         Blocked = bool.Parse(c.Element("Blocked").Value),
                         SeenCount = int.Parse(c.Element("SeenCount").Value)
                       };

或

var query2 = from c in doc.Descendants("SuggestionItem")
                         select new SuggestionItem(c);

我却这样做:

List<SuggestionItem> retList = new List<SuggestionItem>();

var query = from c in doc.Descendants("SuggestionItem") select c;

foreach (XElement item in query)
{
    SuggestionItem anItem = new SuggestionItem(item);
    retList.Add(anItem);
}

这让我可以很容易地调试并找出哪个任务失败了。在这种情况下, XElement 丢失了我在建议项目中解释的字段。

我在2017年与视觉工作室碰见了这些热门节目,同时为新的图书馆例行程序编写单位测试。

友情链接