[[ C#小技巧系列 - 編程 ]]




[[ 排序多維陣列 ]]

例如有個兩維陣列：

1, 6, 7
2, 5, 9
3, 4, 8

如果把它想像成一個Table，當  order by 第2欄 desc  之後，就會變成：

2, 5, 9
3, 4, 8
1, 6, 7


C# 有兩種Array：Jagged Array和Rectangular Array。
Jagged Array其實是個Array of Array，所以只要用 IComparer來定義排序方式便可。

///
using System;
using System.Collections;

public enum SortOrder {
	Ascending
	,Descending
}

public class JaggedComparer: IComparer {
	private int m_SortColumn;
	private SortOrder m_SortOrder;

	public JaggedComparer(int column, SortOrder order) {
		m_SortColumn = column;
		m_SortOrder = order;
	}
	public JaggedComparer(int column) : this(column, SortOrder.Ascending) { }
	public JaggedComparer() : this(0) { }	

	public int Compare(object x, object y) {
		int[] ax = (int[]) x;
		int[] ay = (int[]) y;
		int result;
		
		result = ax[m_SortColumn].CompareTo( ay[m_SortColumn] );
		if (m_SortOrder == SortOrder.Descending) { result *= -1; }
		
		return result;
	}
}

class MainClass {
	static void Main() {
		int[][] a = new int[][] {
			 new int[]{1, 6, 7}
			,new int[]{2, 5, 9}
			,new int[]{3, 4, 8}
		};
		
		Dump2dJaggedArray(a);
		Array.Sort(a, new JaggedComparer(2, SortOrder.Descending));
		Dump2dJaggedArray(a);
	}
	public static void Dump2dJaggedArray( int[][] array)  {
		foreach ( int[] i in array ) {
			foreach ( int j in i ) {
				Console.Write( "{0},", j );
			}
			Console.WriteLine();
		}
		Console.WriteLine();
	}
}
///


至於Rectangular Array，我們可以用間接的方法：


///
using System;
using System.Collections;

public enum SortOrder {
	Ascending
	,Descending
}

public class RectangularComparer: IComparer {
	private int[,] m_OriginalArray;
	private int m_SortColumn;
	private SortOrder m_SortOrder;

	public RectangularComparer(int column, SortOrder order, int[,] array) {
		m_SortColumn = column;
		m_SortOrder = order;
		m_OriginalArray = array;
	}
	public RectangularComparer(int column, int[,] array) : this(column, SortOrder.Ascending, array) { }
	public RectangularComparer(int[,] array) : this(0, array) { }

	public int Compare(object x, object y) {
		int rx = (int) x;
		int ry = (int) y;
		int result;
		
		result = m_OriginalArray[rx, m_SortColumn].CompareTo( m_OriginalArray[ry, m_SortColumn] );
		if (m_SortOrder == SortOrder.Descending) { result *= -1; }
		
		return result;
	}
}

class MainClass {
	static void Main() {
		int[,] a = new int[,] {
			{1, 6, 7}
			,{2, 5, 9}
			,{3, 4, 8}
		};
		int[] rowOrder0 = new int[]{0, 1, 2};
		int[] rowOrder2 = new int[]{0, 1, 2};

		Array.Sort( rowOrder0, new RectangularComparer(0, SortOrder.Descending, a) );
		Array.Sort( rowOrder2, new RectangularComparer(2, SortOrder.Descending, a) );
		
		Dump2dRectangularArray(rowOrder0, a);
		Dump2dRectangularArray(rowOrder2, a);
		
	}
	public static void Dump2dRectangularArray( int[] pRowOrder, int[,] pArray)  {
		for (int i = 0; i < pRowOrder.Length; i++) {
			for (int j = 0; j <= pArray.GetUpperBound(1); j++) {
				Console.Write("{0},",  pArray[pRowOrder[i], j] );
			}
			Console.WriteLine();
		}
		Console.WriteLine();
	}	
}
///


用一個額外的一維陣列 rowOrder2 去儲存行號 0, 1, 2，
當排序時，就排序這個一維陣列。
當存取原本陣列時，就用 rowOrder2 來間接地存取它。

這種間接方式的優點是可以建立多種排序方式，
例如 rowOrder0和rowOrder2，但不用移動原本陣列。
它也可以排序Jagged Array。