Translating a jagged array

Lutoslaw

The code below translates a jagged array. For a jagged array A, the result is a n*m jagged array, where the outer size is n=max(A[i].Length) and the inner size of each subarray is m=A.GetLength(0). Remark: Holes after null or incomplete subarrays will be filled with default(T). Usage:

MyType[][] array = ...;
MyType[][] translated = array.Translate();

For examle: 1.

array = new int[5][] {
new int[] { 5, 6, 7 },
new int [] { 1, 2, 3, 4 },
new int [] { },
new int [] { 0, 1 },
null,
};
expected = new int[4][] {
new int[] { 5, 1, 0, 0, 0 },
new int[] { 6, 2, 0, 1, 0 },
new int[] { 7, 3, 0, 0, 0 },
new int[] { 0, 4, 0, 0, 0 },
};

array = new int[2][] {
null,
null,
};
expected = new int[1][] {
new int[] { 0, 0 },
};

For nullable types, there would be null instead of 0.

public static class JaggedArrayExtensions
{
/// <summary>
/// Translates a given jagged array. Holes after null or incomplete subarrays will be fileld with default(T).
/// </summary>
/// <typeparam name="T">Type of elements in the array</typeparam>
/// <param name="array">The array to translate</param>
/// <returns>A n*m jagged array, where the outer size is n=max(A[i].Length) and
/// the inner size of each subarray is m=A.GetLength(0).</returns>
public static T[][] Translate(this T[][] array)
{
if (array == null)
throw new ArgumentNullException();
if (array.Length == 0)
return new T[0][];
int columnCount = array.Max(sub => sub == null ? 1 : sub.Length);
int rowCount = array.Length;
T[][] res = new T[columnCount][];
for (int i = 0; i < columnCount; i++)
{
res[i] = new T[rowCount];
for (int j = 0; j < rowCount; j++)
{
if (array[j] == null || i >= array[j].Length)
res[i][j] = default(T);
else
res[i][j] = array[j][i];
}
}
return res;
}
}

Greetings - Jacek

Nagy Vilmos

Put this in as a Tip/Trick

Panic, Chaos, Destruction. My work here is done. Drink. Get drunk. Fall over - P O'H OK, I will win to day or my name isn't Ethel Crudacre! - DD Ethel Crudacre I cannot live by bread alone. Bacon and ketchup are needed as well. - Trollslayer Have a bit more patience with newbies. Of course some of them act dumb - they're often *students*, for heaven's sake - Terry Pratchett

Lutoslaw

Done. Hopefully I won't be univoted for cross-posting. However, a Tip/Trick is a different class of post, so I do have an excuse. :cool:

Greetings - Jacek

Lost User

You don't need GetLength(0), because the array is not multidimensional but jagged, so the outer array is "just any old 1D array".

Lutoslaw

:thumbsup: fixed.

Greetings - Jacek

Robert Rohde

How about this one?

public static T[][] Translate2<T>(this T[][] array)
{
if (array == null)
throw new ArgumentNullException();
if (array.Length == 0)
return new T[0][];

return Enumerable.Range(0, array.Max(sub => sub == null ? 1 : sub.Length)).
    Select(i => Enumerable.Range(0, array.Length).
        Select(j => array\[j\] == null || i >= array\[j\].Length ? 
            default(T) : array\[j\]\[i\]).ToArray()).ToArray();

}

Robert

Lost User

No offense, but I would file that under "LINQ where it doesn't help and only slows things down"

Lost User

Also, you don't need to fill holes with default(T). They're already filled with that.

Robert Rohde

I know but its so much fun... :-D

william sharkey

Without data, who knows? If it were done .AsParallel it may be faster on certain system/jagged array combos. Then again, if you find yourself translating jagged arrays on large sets of data, it may be a sign of choosing the wrong data structure.