ArrayHelper.cs

using System;
using System.Collections.Generic;

class ArrayHelper
{   
    static public void OrderBy<T, TKey>(T[] array, SelectHandler<T, TKey> handler)
        where TKey : IComparable,IComparable<TKey>
    {
        for (int i = 0; i < array.Length - 1; i++)
        {
            for (int j = i + 1; j < array.Length; j++)
            {   //arrar[i]: int[],string[],Student[]>zs.age
                //if (array[i].CompareTo(array[j]) > 0)
                if (handler(array[i]).CompareTo(handler(array[j])) > 0)
                {
                    var temp = array[i];
                    array[i] = array[j];
                    array[j] = temp;
                }
            }
        }
    }

    static public void OrderByDescending<T, TKey>(T[] array, SelectHandler<T, TKey> handler)
        where TKey : IComparable, IComparable<TKey>
    {
        for (int i = 0; i < array.Length - 1; i++)
        {
            for (int j = i + 1; j < array.Length; j++)
            {   //arrar[i]: int[],string[],Student[]>zs.age
                //if (array[i].CompareTo(array[j]) > 0)
                if (handler(array[i]).CompareTo(handler(array[j])) < 0)
                {
                    var temp = array[i];
                    array[i] = array[j];
                    array[j] = temp;
                }
            }
        }
    }

    static public T Max<T, TKey>(T[] array, SelectHandler<T, TKey> handler)
        where TKey : IComparable, IComparable<TKey>
    {
        //T max = default(T);
        T max = array[0];
        for (int i = 1; i < array.Length ; i++)
        {                 
            if (handler(max).CompareTo(handler(array[i])) < 0)
            {
                max = array[i];
            }                
        }
        return max;
    }

    static public T Min<T, TKey>(T[] array, SelectHandler<T, TKey> handler)
        where TKey : IComparable, IComparable<TKey>
    {
        //T max = default(T);
        T min = array[0];
        for (int i = 1; i < array.Length; i++)
        {
            if (handler(min).CompareTo(handler(array[i])) > 0)
            {
                min = array[i];
            }
        }
        return min;
    }

    static public T Find<T>(T[] array, FindHandler<T> handler)
    {
        T t = default(T);
        for (int i = 0; i < array.Length; i++)
        {
            if (handler(array[i]))
            { 
                t = array[i]; 
                break; 
            }
        }
        return t;
    }

    static public T[] FindAll<T>(T[] array, FindHandler<T> handler)
    {
        List<T> list = new List<T>();
        for (int i = 0; i < array.Length; i++)
        {
            if (handler(array[i]))
            {                  
                list.Add(array[i]);
            }
        }
        return list.ToArray();
    }

    static public TKey[] Select<T,TKey>(T[] array,SelectHandler<T,TKey> handler)
    {
        TKey[] keys = new TKey[array.Length];
        for (int i = 0; i < array.Length; i++)
        {
            keys[i] = handler(array[i]);
        }
        return keys;
    }    
}

delegate TKey SelectHandler<T,TKey>(T t);//T Student Id,Age,Tall,Name,Book
delegate bool FindHandler<T>(T t);