Converting a Jagged Array to a multidimensional array

Question

I am converting a list within a list to an int[][] using:

int[][] preConvertInts = processedList.Select(array => array.ToArray().ToArray()) as int[][];

I am returning an int[,] in my method. What is the best way to convert an int[][] to an int[,]?

Edit: method

public static int[,] GetIntArrayInts(string dataString){
    string data = dataString;
    data = data.Replace(Environment.NewLine, "\n");

    List<List<int>> processedList = new List<List<int>>();

    string[] rows = data.Split('\n');
    foreach (string row in rows){
        string[] columns = row.Split(',');
        List<int> ints = new List<int>();
        foreach (string column in columns){
            if (int.TryParse(column, out int tileGid)) ints.Add(tileGid);
        }
        processedList.Add(ints);
    }
    int[][] preConvertInts = processedList.Select(array => array.ToArray().ToArray()) as int[][];
    int[,] processedIntArray =  new int[preConvertInts[0].Length, preConvertInts[1].Length];
    for (int i = 0; i < preConvertInts.Length; i++){
        int[] intArray = preConvertInts[i];
        for (int j = 0; j < intArray.Length; j++){
            processedIntArray[i, j] = preConvertInts[i][j];
        }
    }
    return processedIntArray;
}

@mjwills I'm not sure what you're referring to since there is no problem I'm running into. — Luna, Feb 15 '18 at 11:24
@FaizanRabbani I was in the process of adding the method. There you go. — Luna, Feb 15 '18 at 11:27
Refer to this link: https://stackoverflow.com/a/26291720/4222487 — FaizanHussainRabbani, Feb 15 '18 at 11:30

score 5 · Answer 1 · edited Jul 19 '18 at 06:00

5

What is the best way to convert an int[][] to an int[,]?

it is the one that is described in this post. Yours will actually also work if all sub-arrays have the same Length. But to cite you:

Unfortunately, my array is not rectangular. – Luna

Then it would not make much sense to try to convert it. Unless you loose values or you add values to make the dimensions of all sub arrays equal.

But your problem in the code is not this conversion but this one:

I am converting a list within a list to an int[][] using:
int[][] preConvertInts = processedList.Select(array => array.ToArray().ToArray()) as int[][];

This is wrong. You will get null for preConvertInts! if you check the return value of the Select call:

You can see that it returns IEnumerable<int[]> and not int[][]. Casting it with as int[][]; does not work and masks only the fact that the 2 types are different from the compiler. What you do there is to convert each sublist into an array and then convert (the already converted array) simply again into an array.

You need to make the select in the proper way:

int [][] preConvertInts = processedList.Select(x=>x.ToArray()).ToArray();

Explanation:

1) in the first step you collect all sublists and convert each one into an array: Select(x=>x.ToArray())

2) now this call returns an IEnumerable<int[]> which you need to convert again to an array:

Select(x=>x.ToArray()).ToArray();
                     ^^
                     ||
    note the dot behind the closing parentesis of the Select call

edited Jul 19 '18 at 06:00

Luna

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answered Feb 15 '18 at 11:57

Mong Zhu

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Nice, up vote because im eating icecream and its awesome – TheGeneral Feb 15 '18 at 12:02
@MichaelRandall Bon appétit – Mong Zhu Feb 15 '18 at 12:08
@MichaelRandall I added a freehand drawn circle and arrow to the image to make it even more awesome ;) – Mong Zhu Feb 15 '18 at 12:11
1

If i could vote up that arrow i would – TheGeneral Feb 15 '18 at 12:11
This helped. I realised my mistake just a little later. – Luna Feb 15 '18 at 13:02
@Joris glad to hear that it helped. You might consider then to mark it as accepted :) happy coding – Mong Zhu Feb 15 '18 at 14:44
@Luna Hi, that is funny, you come back to this post after 5 months just to change your name in my answer. This post has still not any accepted answer. Did neither post here help you to solve your problem? – Mong Zhu Jul 19 '18 at 07:30

TheGeneral · Answer 2 · 2018-02-15T11:47:38.157

2

Jagged Array

public static T[,] ToMultiArray<T>(this IList<T[]> arrays)
{
    var length = arrays[0].Length;
    var result = new T[arrays.Count, length];
    for (var i = 0; i < arrays.Count; i++)
    {
        var array = arrays[i];
        if (array.Length != length)
        {
            throw new ArgumentException("Misaligned arrays");
        }

        for (var j = 0; j < length; j++)
        {
            result[i, j] = array[j];
        }
    }

    return result;
}

Multidimensional Array

public static T[][] ToJaggedArray<T>(this IList<T[]> arrays)
{

    var result = new T[arrays.Count][];
    for (var i = 0; i < arrays.Count; i++)
    {
        var array = arrays[i];
        var length = array.Length;
        result[i] = new T[length];
        for (var j = 0; j < length; j++)
        {
            result[i][j] = array[j];
        }
    }

    return result;
}

Usage

var preConvertInts = list.ToJaggedArray();

or

var preConvertInts = list.ToMultiArray();

Update

this IList<T[]> arrays this method is for lists which contain arrays, to fit OP's example it should be (this IList<List<T>> arrays) – Mong Zhu

Jagged Array

public static T[][] ToJaggedArray<T>(IList<List<T>> arrays)
{

    var result = new T[arrays.Count][];
    for (var i = 0; i < arrays.Count; i++)
    {
        var array = arrays[i];
        var length = array.Count;
        result[i] = new T[length];
        for (var j = 0; j < length; j++)
        {
            result[i][j] = array[j];
        }
    }

    return result;
}

Multidimensional Array

public static T[,] ToMultiArray<T>(IList<List<T>> arrays)
{
    var length = arrays[0].Count;
    var result = new T[arrays.Count, length];
    for (var i = 0; i < arrays.Count; i++)
    {
        var array = arrays[i];
        if (array.Count != length)
        {
            throw new ArgumentException("Misaligned arrays");
        }

        for (var j = 0; j < length; j++)
        {
            result[i, j] = array[j];
        }
    }

    return result;
}

Note : Totally untested

edited Feb 15 '18 at 11:47

answered Feb 15 '18 at 11:38

TheGeneral

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`this IList arrays` this method is for lists which contain arrays, to fit OP's example it should be `(this IList> arrays)` – Mong Zhu Feb 15 '18 at 11:43
@MongZhu thanks for the heads up – TheGeneral Feb 15 '18 at 11:44
otherwise your method works. But so does the one in the duplicate :) – Mong Zhu Feb 15 '18 at 11:47
@MongZhu i have no idea! – TheGeneral Feb 15 '18 at 11:48
@MongZhu thanks for the help :) – TheGeneral Feb 15 '18 at 11:48
in `ToMultiArray` you could also check all sub arrays dimensions in the beginning : `if (arrays.Select(x => x.Count()).Distinct().Count() > 1)` and skip then the entire iteration if the dimension do not fit – Mong Zhu Feb 15 '18 at 11:50
These methods are useful. Unfortunately, my array is not rectangular. – Luna Feb 15 '18 at 11:52
@MongZhu also good point – TheGeneral Feb 15 '18 at 11:52
@Joris the jagged array one will work for you – TheGeneral Feb 15 '18 at 11:56
@Joris then it does not make sense for you to convert it into a multi dimensional array – Mong Zhu Feb 15 '18 at 11:58
`length` shouldn't be `arrays.Max(e => e.Count)`? Since a `List` at index 0 could have less elements than the longest list inside of `arrays`. – mrogal.ski Feb 15 '18 at 12:16
1

@m.rogalski i guess in this example the multi version expects the same length, but you raise a good points, it could just creat the biggest occurrence and default up the type for anything missing – TheGeneral Feb 15 '18 at 12:24

Converting a Jagged Array to a multidimensional array

2 Answers2

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