How to store and handle large arrays in unity

Question

In my unity project, I have a very large array of arrays of integers. It contains around 65 thousand arrays each of length 4. When I attempt to use this in my program, it crashes and unity shuts down.

I want to be able to quickly get the nth array within the array, and don't need to be able to edit it or anything. What is the best way to store and handle the data?

Answer 1

I sort of found a solution. I put all the information as lines of numbers in a .txt file, which actually only ended up being around 370KB big, and then used the following script to transfer this into an int[][].

using UnityEngine;
using System.IO;

public static class TranpositionTable
{
    public static string[] data;
    public static string[][] seperatedData;
    public static int[][] intData;

    static TranpositionTable()
    {
        string path = Application.dataPath + "/Scripts/TranspositionTable/table.txt";
        data = File.ReadAllText(path).Split("\n");
        seperatedData = new string[data.Length][];
        for (int i = 0; i < data.Length; i++)
        {
            seperatedData[i] = data[i].Split(",");
        }
        intData = new int[seperatedData.Length][];
        for (int i = 0; i < seperatedData.Length; i++)
        {
            if (seperatedData[i][0] == "n")
            {
                intData[i] = null;
            }
            else
            {
                intData[i] = new int[4];
                for (int j = 0; j < seperatedData[i].Length; j++)
                {
                    intData[i][j] = int.Parse(seperatedData[i][j]);
                }
            }
        }
    }

}

This is then referenced in other scripts with

using static TranpositionTable;

I thought that this would be slower then just having an int[][] with all the numbers in it, but there haven't been any performance problems, so I guess its fine.

Answer 2

You should probably use an array of a value type, perhaps something like

public readonly struct Vector4i{
    public int X {get; init;} 
    public int Y {get; init;} 
    public int Z {get; init;} 
    public int W {get; init;} 
}

Arrays are objects, and objects have overhead. Each array will require 16 bytes of extra memory, + 8 bytes for the reference (on x64). So you will almost double the required memory compared with a struct. You will also make life much more difficult for the GC since it has tons of references it needs to follow. It may also impair cache locality, since there is no guarantee adjacent arrays are stored adjacent in memory.

Using value types for fixed-size data removes all of this overhead, giving you a single continuous memory chunk of about ~1Mb.

Note that it may be possible to use Span<T> this provide an abstraction over some sequence of data. You should be able to convert your array to a ReadOnlySpan<int>, and then slice this down to a single vector. These conversions would essentially be free. There are also ways to prevent unnecessary copies, like the in parameter modifier.