Jagged Array is always empty

Question

I can't seem to figure out why item within a List is not being appended to a Jagged Array.

I have the following code

var list = new List<(double,double)>{                
          ( -99.8299313, 32.2840118),
          ( -99.8293304, 32.2840118),
};

var jaggedArray = new double[list.Count()][];
foreach (var item in list)
{
   var s = item.Split(",");
   jaggedArray.Append(new string[] { 
              Convert.ToDouble(s[0]), 
              Convert.ToDouble(s[1]) })
                     .ToArray();
}

When I inspect the array it's empty? What am I doing wrong?

I have even declared the size of the array using list.Count() but its always empty?

This does not even compile (because `(double,double)` is not a string, I assume). — Guru Stron, Apr 05 '23 at 19:22

Guru Stron · Accepted Answer · 2023-04-05T19:35:05.997

From Enumerable.Append docs:

This method does not modify the elements of the collection. Instead, it creates a copy of the collection with the new element.

Which is demonstrated by the code sample there:

// Creating a list of numbers
List<int> numbers = new List<int> { 1, 2, 3, 4 };

// Trying to append any value of the same type
numbers.Append(5);

// It doesn't work because the original list has not been changed
Console.WriteLine(string.Join(", ", numbers));

// It works now because we are using a changed copy of the original list
Console.WriteLine(string.Join(", ", numbers.Append(5)));

// If you prefer, you can create a new list explicitly
List<int> newNumbers = numbers.Append(5).ToList();

// And then write to the console output
Console.WriteLine(string.Join(", ", newNumbers));

// This code produces the following output:
//
// 1, 2, 3, 4
// 1, 2, 3, 4, 5
// 1, 2, 3, 4, 5

So one thing you can do is reassign the jaggedArray (after fixing the issue I've mentioned in the comment):

jaggedArray = jaggedArray.Append(new string[] { s[0], s[1] }).ToArray();

Though it would not be the most effective approach. A better one would be to just go with LINQ all the way:

List<string> list = ...;

var jaggedArray = list
    .Select(s => s.Split(","))
    .Select(s => new string[] { s[0], s[1] }) 
    .ToArray();

Note that new string[] { s[0], s[1] } will throw if there is less than 2 elements, consider using Where(s => s.Length > 1) to filter out such cases if appropriate.

Jagged Array is always empty

1 Answers1