Add item at the beginning of each inner array in jagged array

Question

So, there is a big jagged string array (~ [120] [1 000 000]) here that represents data from an excel worksheet ( columns / rows).

Task: We have to append items at the beginning of each inner array.

I have a solution, but I am not sure about performance.

private string[][] AddField(string[][] exportDataFieldValues, string linkDisplayFieldValue)
    {
        var newExportDataFieldValues = new List<string[]>();
        foreach (var row in exportDataFieldValues)
        {
            var cellsRange = row.ToList();
            cellsRange.Insert(0, linkDisplayFieldValue);

            newExportDataFieldValues.Add(cellsRange.ToArray());
        }

        return newExportDataFieldValues.ToArray();
    }

Q: As you can see, my solution contains a lot of type conversions, I believe there is a more effective solution. Сan you provide a more effective solution?

Answer 1

I guess your code will behave very bad performance wise.
I would suggest to create the cellsRange object first as a List<whatever> and add 0,linkDisplayFieldValue first and then call AddRange() on cellsRange passing row.ToList() as parameter.

Answer 2

You could model your data as an array of List, and encapsulate it in a class, such that all access to the data is only via the class properties and methods.

When initializing this class, reverse the columns to populate the lists. Then to logically add an item to the front, you can instead append to the end of the list, which is quite efficient.

The members of this class should abstract away that fact that the columns are actually stored in reverse order and compute the actual index of the column by subtracting from the number of items in the list. (List.Count() - Idx - 1).