Convert a C# jagged array to an array and back again

Question

I currently have a jagged array Class[][][] which I want to serialise as a normal Class[] array, then convert back into a Class[][][] array after deserialization. Is it at all possible to convert between the two both ways? The dimensions are of constant sizes.

Answer 1

This is how you can flatten to a 1-dimensional structure:

var jagged = new object[][][];
var flattened = jagged.SelectMany(inner => inner.SelectMany(innerInner => innerInner)).ToArray();

As for going back to multidimensional - this will depend entirely on what it is your trying to achieve/what the data represents

Answer 2

If you don't mind serializing a flattened array and an array of ints, you can use the following:

public static int[] JaggedSizes<T>(this T[][][] topArray)
{
    List<int> rtn = new List<int>();
    rtn.Add(topArray.Length);
    for (int i = 0; i < topArray.Length; i++)
    {
        var midArray = topArray[i];
        rtn.Add(midArray.Length);
        for (int j = 0; j < midArray.Length; j++)
        {
            var botArray = midArray[j];
            rtn.Add(botArray.Length);
        }
    }
    return rtn.ToArray();
}

// Thanks @Dave Bish
public static T[] ToFlat<T>(this T[][][] jagged)
{
    return jagged.SelectMany(inner => 
        inner.SelectMany(innerInner => innerInner)).ToArray(); 
}

public static T[][][] FromFlatWithSizes<T>(this T[] flat, int[] sizes)
{
    int inPtr = 0;
    int sPtr = 0;
    int topSize = sizes[sPtr++];
    T[][][] rtn = new T[topSize][][];
    for (int i = 0; i < topSize; i++)
    {
        int midSize = sizes[sPtr++];
        T[][] mid = new T[midSize][];
        rtn[i] = mid;
        for (int j = 0; j < midSize; j++)
        {
            int botSize = sizes[sPtr++];
            T[] bot = new T[botSize];
            mid[j] = bot;
            for (int k = 0; k < botSize; k++)
            {
                bot[k] = flat[inPtr++];
            }
        }
    }
    return rtn;
}