converting List<List<string[]>> into string [][][] in c#

Question

When creating webservices, in c#, I have found it very useful to pass back jagged arrays, i.e. string[][]

I also found a neat trick to build these in a simple way in my code, which was to create a List and convert it by doing a ToArray() call.

e.g.

public string[][] myws() {
    List<string[]> output = new List<string[]>();
    return output.ToArray();
}

I would like to be able to employ a similar solution, but I can't think how to do something similar with a 3 level jagged array or string[][][], without resorting to loops and such.

Regards Martin

James Michael Hare · Accepted Answer · 2012-07-05 16:27:18Z

6

You can get there by doing a Select() which converts each inner List<string> to an array using ToArray(), and then converting those results using ToArray():

        var x = new List<List<string[]>>();

        string[][][] y = x.Select(a => a.ToArray()).ToArray();

And so on for as many levels deep as you'd want to go.

answered Jul 5, 2012 at 16:27

James Michael Hare

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5 Comments

Robert Levy Over a year ago

to be clear this isn't avoiding "loops and such", it's just burying the implementation of those loops inside of LINQ. it's the right answer though.

James Michael Hare Over a year ago

@RobertLevy: True, it only avoids loops in the sense of having a cleaner appearance, internally, yes it still loops -- unfortunately any conversion from a list to an array at some point performs loops either explicitly or implicitly...

D Stanley Over a year ago

@RobertLevy: Actually, List<T>.ToArray() just does an Array.Copy() since the underlying storage for a List<T> is already an Array.

James Michael Hare Over a year ago

@DStanley: Good to know, I forgot List<T> already had a ToArray() implementation...

Servy Over a year ago

@DStanley And that will, at some level, still be performing a loop. It might be a more efficient loop if it's at a lower level, but at some point each bit of data in the list is being copied to a new location. The point here is mostly that the operation is, at best, O(sizeOfDimention^numberOfDimensions). It's not O(1) the way some people think that it might be.

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