C# SelectMany Example - Cartesian Product

CartesianProductSelectManyExample.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

public class CartesianProductSelectManyExample
{
	public static void Main(string[] args)
	{
		var abcArray = new string[]{"a", "b", "c"};
		var xyzArray = new string[]{"x", "y", "z"};
	
		var combos = CartesianProductSmart(abcArray, xyzArray);

		foreach(var combo in combos)
		{
			Console.WriteLine(string.Format("[{0},{1}]", combo[0], combo[1]));
		}
	}

	private static string[][] CartesianProductSmart(string[] arr1, string[] arr2)
	{
		// for each s1 in arr1, extract arr2, 
		// then pass s1 and s2 into a newly-made string array.
		return arr1.SelectMany(s1 => arr2, (s1, s2) => new string[]{s1, s2})
			.ToArray();
	}

	private static string[][] CartesianProductDumb(string[] arr1, string[] arr2)
	{
		// the dumb way; nested foreach
		string[][] combos = new string[arr1.Length * arr2.Length][];

		int ii = 0;
		foreach(var strOne in arr1)
		{
			foreach(var strTwo in arr2)
			{
				string[] combo = new string[2];

				combo[0] = strOne;
				combo[1] = strTwo;
				combos[ii] = combo;

				ii++;
			}
		}

		return combos;
	}
}