版权声明：本文为云勇原创文章，转载请注明来源于云勇博客 https://blog.csdn.net/yongyong521/article/details/78947463
// /***********************************************************
// * 项目名称： YunDouTax.BaseLib
// * 文件名称： EnumerableExtension.cs
// * 功能描述：
// * 代码作者： 云勇
// * 创建时间： 2017年12月25日 11:50
// * 更新时间： 2018年01月01日 21:12
// ************************************************************/
namespace YunDouTax.BaseLib.Extensions
{
/// <summary>
/// 提供一组用于查询实现 System.Collections.Generic.IEnumerable`1 的对象的 static 方法。
/// </summary>
public static class EnumerableExtension
{
/// <summary>
/// 通过合并元素的索引将序列的每个元素投影到新表中。
/// </summary>
/// <typeparam name="TSource">The type of the source.</typeparam>
/// <typeparam name="TResult">The type of the result.</typeparam>
/// <param name="source">The source.</param>
/// <param name="selector">The selector.</param>
/// <returns></returns>
/// <exception cref="System.ArgumentNullException">selector cann't be null.</exception>
public static IEnumerable<TResult> Select<TSource, TResult>(this IEnumerable<TSource> source, Func<TSource, TResult> selector)
{
if (selector == null)
{
throw new ArgumentNullException("selector cann't be null.");
}
foreach (TSource item in source)
{
if (item == null)
{
continue;
}
TResult result = selector(item);
if (result == null)
{
continue;
}
yield return result;
}
}
/// <summary>
/// 基于谓词筛选值序列。
/// </summary>
/// <typeparam name="TSource">The type of the source.</typeparam>
/// <param name="source">The source.</param>
/// <param name="predicate">The predicate.</param>
/// <returns></returns>
/// <exception cref="System.ArgumentNullException">predicate cann't be null.</exception>
public static IEnumerable<TSource> Where<TSource>(this IEnumerable<TSource> source, Func<TSource, bool> predicate)
{
if (predicate == null)
{
throw new ArgumentNullException("predicate cann't be null.");
}
foreach (TSource item in source)
{
if (predicate(item))
{
yield return item;
}
}
}
/// <summary>
/// 返回序列中的元素数量。
/// </summary>
/// <typeparam name="TSource">The type of the source.</typeparam>
/// <param name="source">The source.</param>
/// <returns></returns>
public static int Count<TSource>(this IEnumerable<TSource> source)
{
int count = 0;
foreach (TSource item in source)
{
count++;
}
return count;
}
/// <summary>
/// 返回一个数字，表示在指定的序列中满足条件的元素数量。
/// </summary>
/// <typeparam name="TSource">The type of the source.</typeparam>
/// <param name="source">The source.</param>
/// <param name="predicate">The predicate.</param>
/// <returns></returns>
/// <exception cref="System.ArgumentNullException">predicate cann't be null.</exception>
public static int Count<TSource>(this IEnumerable<TSource> source, Func<TSource, bool> predicate)
{
if (predicate == null)
{
throw new ArgumentNullException("predicate cann't be null.");
}
int count = 0;
foreach (TSource item in source)
{
if (predicate(item))
{
count++;
}
}
return count;
}
/// <summary>
/// 返回序列中的第一个元素；如果序列中不包含任何元素，则返回默认值。
/// </summary>
/// <typeparam name="TSource">The type of the source.</typeparam>
/// <param name="source">The source.</param>
/// <param name="predicate">The predicate.</param>
/// <returns></returns>
public static TSource FirstOrDefault<TSource>(this IEnumerable<TSource> source, Func<TSource, bool> predicate = null)
{
if (source == null)
{
return default(TSource);
}
foreach (TSource item in source)
{
if (predicate == null)
{
return item;
}
if (predicate != null && predicate(item))
{
return item;
}
}
return default(TSource);
}
/// <summary>
/// 从 System.Collections.Generic.IEnumerable`1 创建一个 System.Collections.Generic.List`1。
/// </summary>
/// <typeparam name="TSource">The type of the source.</typeparam>
/// <param name="source">The source.</param>
/// <returns></returns>
public static List<TSource> ToList<TSource>(this IEnumerable<TSource> source)
{
return new List<TSource>(source);
}
/// <summary>
/// 从 System.Collections.Generic.IEnumerable`1 创建一个数组。
/// </summary>
/// <typeparam name="TSource">The type of the source.</typeparam>
/// <param name="source">The source.</param>
/// <returns></returns>
public static TSource[] ToArray<TSource>(this IEnumerable<TSource> source)
{
TSource[] array = new TSource[source.Count()];
int index = 0;
foreach (TSource item in source)
{
array[index++] = item;
}
return array;
}
/// <summary>
/// 通过使用默认的相等比较器确定序列是否包含指定的元素。
/// </summary>
/// <typeparam name="TSource">The type of the source.</typeparam>
/// <param name="source">The source.</param>
/// <param name="value">The value.</param>
/// <returns>
/// <c>true</c> if [contains] [the specified value]; otherwise, <c>false</c>.
/// </returns>
public static bool Contains<TSource>(this IEnumerable<TSource> source, TSource value)
{
foreach (TSource item in source)
{
if (item.Equals(value))
{
return true;
}
}
return false;
}
/// <summary>
/// 判断指定的序列是否为空
/// </summary>
/// <typeparam name="TSource">The type of the source.</typeparam>
/// <param name="source">The source.</param>
/// <returns>
/// <c>true</c> if the specified source is empty; otherwise, <c>false</c>.
/// </returns>
public static bool IsEmpty<TSource>(this IEnumerable<TSource> source)
{
return source == null || source.Count() == 0;
}
/// <summary>
/// 根据键按升序对序列的元素排序
/// </summary>
public static IEnumerable<TSource> OrderBy<TSource, TKey>(this IEnumerable<TSource> source, Func<TSource, TKey> keySelector) where TKey : IComparable
{
List<TSource> ls = source.ToList();
for (int i = 0; i < ls.Count; i++)
{
TKey min = keySelector(ls[i]);
for (int j = i + 1; j < ls.Count; j++)
{
TKey key = keySelector(ls[j]);
if (min.CompareTo(key) > 0)
{
min = key;
TSource tmp = ls[i];
ls[i] = ls[j];
ls[j] = tmp;
}
}
yield return ls[i];
}
}
/// <summary>
/// Alternates the specified first.
/// </summary>
/// <typeparam name="TSource">The type of the source.</typeparam>
/// <param name="first">The first.</param>
/// <param name="second">The second.</param>
/// <returns></returns>
public static IEnumerable<TSource> Alternate<TSource>(this IEnumerable<TSource> first, IEnumerable<TSource> second)
{
using (IEnumerator<TSource> e1 = first.GetEnumerator())
using (IEnumerator<TSource> e2 = second.GetEnumerator())
{
while (e1.MoveNext() && e2.MoveNext())
{
yield return e1.Current;
yield return e2.Current;
}
}
}
/// <summary>
/// Appends the specified source.
/// </summary>
/// <typeparam name="TSource">The type of the source.</typeparam>
/// <param name="source">The source.</param>
/// <param name="element">The element.</param>
/// <returns>IEnumerable<TSource></returns>
public static IEnumerable<TSource> Append<TSource>(this IEnumerable<TSource> source, TSource element)
{
using (IEnumerator<TSource> e1 = source.GetEnumerator())
{
while (e1.MoveNext())
{
yield return e1.Current;
}
}
yield return element;
}
/// <summary>
/// Determines whether [contains] [the specified source].
/// </summary>
/// <typeparam name="TSource">The type of the source.</typeparam>
/// <typeparam name="TResult">The type of the result.</typeparam>
/// <param name="source">The source.</param>
/// <param name="value">The value.</param>
/// <param name="selector">The selector.</param>
/// <returns>
/// <c>true</c> if [contains] [the specified source]; otherwise, <c>false</c>.
/// </returns>
public static bool Contains<TSource, TResult>(this IEnumerable<TSource> source, TResult value, Func<TSource, TResult> selector)
{
foreach (TSource sourceItem in source)
{
TResult sourceValue = selector(sourceItem);
if (sourceValue.Equals(value))
{
return true;
}
}
return false;
}
/// <summary>
/// Prepends the specified source.
/// </summary>
/// <typeparam name="TSource">The type of the source.</typeparam>
/// <param name="source">The source.</param>
/// <param name="element">The element.</param>
/// <returns>IEnumerable<TSource></returns>
public static IEnumerable<TSource> Prepend<TSource>(this IEnumerable<TSource> source, TSource element)
{
yield return element;
using (IEnumerator<TSource> e1 = source.GetEnumerator())
{
while (e1.MoveNext())
{
yield return e1.Current;
}
}
}
}
}