All()：判断所有元素是否都满足条件，若有一个不满足就返回false，否则返回true，源代码如下，如果方法里参数均为null，则会抛出异常。若该对象为null也会抛出异常，若该IEnumbe类型里元素个数为0，则会一直返回true

public static bool All
      
       (this IEnumerable
       
         source, Func
        
          predicate) {            if (source == null) throw Error.ArgumentNull("source");            if (predicate == null) throw Error.ArgumentNull("predicate");            foreach (TSource element in source) {                if (!predicate(element)) return false;            }            return true;        }
        
       
      

Any()：如下判断对象里是否有元素，若集合为null，则会报错 public static bool Any
     
      (this IEnumerable
      
        source) {            if (source == null) throw Error.ArgumentNull("source");            using (IEnumerator
       
         e = source.GetEnumerator()) {                if (e.MoveNext()) return true;            }            return false;        } 如下判断对象里是否存在满足某条件的，若满足为true，否则为false   若对象为null，则会报错
       
      
     

public static bool 
     
      (this 
      
        source, 
       
         predicate) {            if (source == null) throw Error.ArgumentNull("source"); if (predicate == null) throw Error.ArgumentNull("predicate"); foreach (TSource element in source) { if (predicate(element)) return true; } return false; }
       
      
     

Average  求平均值  若集合为Null，则会抛出异常,若集合中没有元素，则也会抛出异常

public static double (this 
     
       source) {            if (source == null) throw Error.ArgumentNull("source");            long sum = 0;            long count = 0;            checked {                foreach (int v in source) { sum += v; count++; } } if (count > 0) return (double)sum / count; throw Error.NoElements(); }
     

public static double? (this 
     
       source) {            if (source == null) throw Error.ArgumentNull("source");            long sum = 0;            long count = 0;            checked {                foreach (int? v in source) { if (v != null) { sum += v.(); count++; } } } if (count > 0) return (double)sum / count; return null; }
     

 

LastOrDefault/FirstOrDefault  返回第一个元素，若没有元素，则返回元素的默认值，若集合为Null,则抛出异常，LastOrDefault 相反 First/Last 返回第一个或者最后一个元素，若集合为中没有元素，则抛出异常 Single/SingleOrDefault 返回序列的唯一元素，若存在多个元素，则都报错，若集合为null，则 SingleOrDefault 返回默认值

public static TSource 
     
      (this 
      
        source) {            if (source == null) throw Error.ArgumentNull("source"); 
       
         list = source as 
        
         ; if (list != null) { if (list. > 0) return list[0]; } else { using (
         
           e = source.()) { if (e.()) return e.; } } return default(TSource); } 满足条件的第一个元素
         
        
       
      
     

public static TSource 
     
      (this 
      
        source, 
       
         predicate) { if (source == null) throw Error.ArgumentNull("source"); if (predicate == null) throw Error.ArgumentNull("predicate"); foreach (TSource element in source) { if (predicate(element)) return element; } return default(TSource); }
       
      
     

ToList/toArray/ToDictionary 

public static 
      
      
       (this 
       
         source) {            if (source == null) throw Error.ArgumentNull("source"); return new 
        
         (source); }
        
       
      
     

LongCount/Count 返回元素个数，若集合为Null,则抛出异常

public static int 
     
      (this 
      
        source) {            if (source == null) throw Error.ArgumentNull("source");            
       
         collectionoft = source as 
        
         ; if (collectionoft != null) return collectionoft.; collection = source as ; if (collection != null) return collection.; int count = 0; using (
         
           e = source.()) { checked { while (e.()) count++; } } return count; }
         
        
       
      
     

Containspublic static bool Contains
     
      (this IEnumerable
      
        source, TSource value) {            ICollection
       
         collection = source as ICollection
        
         ;            if (collection != null) return collection.Contains(value);            return Contains
         
          (source, value, null);        }         public static bool Contains
          
           (this IEnumerable
           
             source, TSource value, IEqualityComparer
            
              comparer) { if (comparer == null) comparer = EqualityComparer
             
              .Default; if (source == null) throw Error.ArgumentNull("source"); foreach (TSource element in source) if (comparer.Equals(element, value)) return true; return false; }
             
            
           
          
         
        
       
      
     

Concat

blic static 
      
      
       (this 
       
         first, 
        
          second) { if (first == null) throw Error.ArgumentNull("first"); if (second == null) throw Error.ArgumentNull("second"); return 
         
          (first, second); } static 
           
           
            (
            
              first, 
             
               second) { foreach (TSource element in first) yield return element; foreach (TSource element in second) yield return element; }
             
            
           
          
         
        
       
      
     

Distinct

public static 
      
      
       (this 
       
         source) {            if (source == null) throw Error.ArgumentNull("source"); return 
        
         (source, null); } public static 
          
          
           (this 
           
             source, 
            
              comparer) { if (source == null) throw Error.ArgumentNull("source"); return 
             
              (source, comparer); } static 
               
               
                (
                
                  source, 
                 
                   comparer) { 
                  
                    set = new 
                   
                    (comparer); foreach (TSource element in source) if (set.(element)) yield return element; }
                   
                  
                 
                
               
              
             
            
           
          
         
        
       
      
     

ElementAt /ElementAtOrDefault  返回某个索引处的元素，第一个若索引不存在，则抛出异常，第二个方法若索引越界，则返回元素的默认值。

Except 返回集合差集  Union 返回集合并集  Intersect返回交集

Max/Min 返回集合的最大值和最小值 Sum求和