GroupBy操作
时间：2010-08-17 来源：kis$ove
Linq GroupBy操作
#region GroupBy Operator
/* GroupBy第一种原型
*
* 返回值为IGroupting<K,T>集合数组,每个IGroupting<k,t>包含一个(K)Key及
* 一个拥有相同Key的集合数组T
*
* 将含有相同的Key 分成一组
* public static IEnumerable<IGrouping<K, T>> GroupBy<T, K>(
* this IEnumerable<T> source,
* Func<T, K> keySelector);
*
*/
static void GroupByFirstPrototype()
{
PresidentsOption[] presidentsOptions ={new PresidentsOption(1,10),
new PresidentsOption(2,10),
new PresidentsOption(2,50),
new PresidentsOption(3,100),
new PresidentsOption(4,30),
new PresidentsOption(4,80),
new PresidentsOption(5,200),
new PresidentsOption(5,10),
new PresidentsOption(6,90),
new PresidentsOption(6,80),
new PresidentsOption(7,10)};
IEnumerable<IGrouping<int, PresidentsOption>> outerSequence = presidentsOptions.GroupBy(p => p.Id);
foreach (IGrouping<int, PresidentsOption> keyGroupSequence in outerSequence)
{
Console.WriteLine("-----------------------------------");
Console.WriteLine("....key(id):" + keyGroupSequence.Key);
foreach (PresidentsOption presidents in keyGroupSequence)
{
Console.WriteLine("id={0}...option={1}", presidents.Id, presidents.Option);
}
}
}
/*GroupBy第二种原型
*
* 功能和第一种一样,只是比较方法 comparer自定义
* 需要实现IEqualityComparer<K>接口
*
* public static IEnumerable<IGrouping<K, T>> GroupBy<T, K>(
* this IEnumerable<T> source,
* Func<T, K> keySelector,
* IEqualityComparer<K> comparer);
*
*/
static void GroupBySecondPrototype()
{
PresidentsOption[] presidentsOptions ={new PresidentsOption(1,10),
new PresidentsOption(2,10),
new PresidentsOption(2,50),
new PresidentsOption(3,100),
new PresidentsOption(4,30),
new PresidentsOption(4,80),
new PresidentsOption(5,200),
new PresidentsOption(5,10),
new PresidentsOption(6,90),
new PresidentsOption(6,80),
new PresidentsOption(7,10)};
GroupByCompare compare=new GroupByCompare();
//通过compare比较.具有相同hashCode的Key分成一组
IEnumerable<IGrouping<int, PresidentsOption>> outerSequence = presidentsOptions.GroupBy(p => p.Id, compare);
foreach (IGrouping<int, PresidentsOption> keyGroupSequence in outerSequence)
{
Console.WriteLine("-----------------------------------");
Console.WriteLine("....key(hashCode):" + keyGroupSequence.Key);
foreach (PresidentsOption presidents in keyGroupSequence)
{
Console.WriteLine("id={0}...option={1}" , presidents.Id, presidents.Option);
}
}
}
/* GroupBy第三种原型
*
* 第三钟原型和第一种类似,只不过IGrouping<K, E>中E值为T的一个元素,
* 而不是是T类型的实体对象
*
* public static IEnumerable<IGrouping<K, E>> GroupBy<T, K, E>(
* this IEnumerable<T> source,
* Func<T, K> keySelector,
* Func<T, E> elementSelector);
*
*/
static void GroupByThirdPrototype()
{
PresidentsOption[] presidentsOptions ={new PresidentsOption(1,10),
new PresidentsOption(2,10),
new PresidentsOption(2,50),
new PresidentsOption(3,100),
new PresidentsOption(4,30),
new PresidentsOption(4,80),
new PresidentsOption(5,200),
new PresidentsOption(5,10),
new PresidentsOption(6,90),
new PresidentsOption(6,80),
new PresidentsOption(7,10)};
IEnumerable<IGrouping<int, int>> outerSequence = presidentsOptions.GroupBy(p => p.Id,p=>p.Option);
foreach (IGrouping<int, int> keyGroupSequence in outerSequence)
{
Console.WriteLine("-----------------------------------");
Console.WriteLine("....key(id):" + keyGroupSequence.Key);
foreach (int options in keyGroupSequence)
{
Console.WriteLine("...option={0}", options);
}
}
}
/*GroupBy第四种原型
*
*
* 第四种具有第二种和第三中功能
*
* public static IEnumerable<IGrouping<K, E>> GroupBy<T, K, E>(
* this IEnumerable<T> source,
* Func<T, K> keySelector,
* Func<T, E> elementSelector,
* IEqualityComparer<K> comparer);
*
*/
static void GroupByFourthPrototype()
{
PresidentsOption[] presidentsOptions ={new PresidentsOption(1,10),
new PresidentsOption(2,10),
new PresidentsOption(2,50),
new PresidentsOption(3,100),
new PresidentsOption(4,30),
new PresidentsOption(4,80),
new PresidentsOption(5,200),
new PresidentsOption(5,10),
new PresidentsOption(6,90),
new PresidentsOption(6,80),
new PresidentsOption(7,10)};
GroupByCompare compare = new GroupByCompare();
IEnumerable<IGrouping<int, int>> outerSequence = presidentsOptions.GroupBy(p => p.Id, p => p.Option,compare);
foreach (IGrouping<int, int> keyGroupSequence in outerSequence)
{
Console.WriteLine("-----------------------------------");
Console.WriteLine("....key(hashCode):" + keyGroupSequence.Key);
foreach (int options in keyGroupSequence)
{
Console.WriteLine("...option={0}", options);
}
}
}
#endregion
用到的类：
public class PresidentsOption
{
public int Id
{
get;
set;
}
public int Option
{
get;
set;
}
public PresidentsOption(int id, int option)
{
this.Id = id;
this.Option = option;
}
}
//实现IEqualityComparer<T>
public class GroupByCompare : IEqualityComparer<int>
{
public bool Equals(int x, int y)
{
return (isLessFive(x) == isLessFive(y));
}
//小于返回1的HashCode、大于等于5的返回5的hashCode
public int GetHashCode(int x)
{
int intStart = 1;
int intCompare = 5;
return isLessFive(x) ? intStart.GetHashCode() : intCompare.GetHashCode();
}
public bool isLessFive(int x)
{
return (x < 5);
}
}
本文来自CSDN博客，转载请标明出处：http://blog.csdn.net/Feiin/archive/2008/08/06/2778000.aspx
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