How do I search for the index of an int[2] in a list?

Question

So, I'm poking around at being able to search for the index of an int[2] in a list but I haven't had much luck.

Below is the code I've been playing with:

var coordinates = new List<int[]>();
coordinates.Add(new int[] { 1, 2 });
coordinates.Add(new int[] { 3, 4 });
coordinates.Add(new int[] { 5, 6 });

//foreach (int[] array in coordinates)
//{
//    Console.WriteLine(string.Join(", ", array));
//}

coordinates.AddRange(new int[3][] { [7, 8], [9, 10], [11, 12] });
foreach (int[] array in coordinates)
{
    Console.WriteLine(string.Join(", ", array));
}

//var index = coordinates.IndexOf([3,4]);
var index = coordinates.IndexOf(new int[] { 3, 4 });
Console.WriteLine(index);

Both the above IndexOf lines have returned a value of -1 so I assume my syntax is wrong (or I'm using the wrong tools, which is also possible). Any suggestions?

Answer 1

IndexOf method will not work directly on array elements since it uses the Equals method for arrays. This checks for reference equality rather than content equality. Therefore, you need to compare the contents of the arrays manually.

So, instead of using int array I would prefer values represented as strings which makes easy to find the index of the value.

using System.Collections.Generic;

var coordinates = new List<string>();
coordinates.Add("1,2");
coordinates.Add("3,4");
coordinates.Add("5,6");
coordinates.Add("7,8");
coordinates.Add("9,10");
coordinates.Add("11,12");

foreach (string item in coordinates)
{
    Console.WriteLine(item);
}

var _valueToSearch = "7,8";
var index = coordinates.IndexOf(_valueToSearch);
Console.WriteLine(index);

Also, you may try to implement your own search logic some thing like this:

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

class Program
{
    static void Main()
    {
        var coordinates = new List<int[]>();
        coordinates.Add(new int[] { 1, 2 });
        coordinates.Add(new int[] { 3, 4 });
        coordinates.Add(new int[] { 5, 6 });
        coordinates.AddRange(new int[3][] { new int[] { 7, 8 }, new int[] { 9, 10 }, new int[] { 11, 12 } });

        foreach (int[] array in coordinates)
        {
            Console.WriteLine(string.Join(", ", array));
        }

        var _valueToSearch = new int[] { 3, 4 };

        int index = FindIndex(coordinates, _valueToSearch);
        Console.WriteLine(index);
    }

    static int FindIndex(List<int[]> list, int[] valueToSearch)
    {
        for (int i = 0; i < list.Count; i++)
        {
            if (AreArraysEqual(list[i], valueToSearch))
            {
                return i;
            }
        }
        return -1; // Not found
    }

    static bool AreArraysEqual(int[] array1, int[] array2)
    {
        if (array1.Length != array2.Length)
        {
            return false;
        }

        for (int i = 0; i < array1.Length; i++)
        {
            if (array1[i] != array2[i])
            {
                return false;
            }
        }

        return true;
    }
}