How to cast object[] to double[][] in C#

Question

I have something like

var a = new object[2]
{
     new double[1] { 0.5 },
     new double[1] { 0.5 }
}

And I want to cast this to double[][]. I tried (double[][])a and a.Cast<double[][]>() but it didnt work

It isn't either of things though. For example, you could write a[0] = "Hello"; and that would be entirely valid. — Jon Skeet
– Jon Skeet, Commented Jan 23, 2023 at 12:42
When you know for sure its a double[][] so you can cast it why isn't it of that type in the first place? — Ralf
– Ralf, Commented Jan 23, 2023 at 12:49
@Ralf because I get the result from an external API, that could only pass me objects — sausage_mouse
– sausage_mouse, Commented Jan 23, 2023 at 12:53

Heinzi · Accepted Answer · 2023-01-23 12:56:07Z

6

Your attempt of doing a.Cast<double[][]>() is almost correct. You can use:

double[][] b = a.Cast<double[]>().ToArray();

Explanation:

The problem is that the elements of your list are double[]s, but they are statically typed as object. To change the static type of a list's elements, you use LINQ's Cast<T>.
Cast<T> takes the type of the element as T, not the type of the resulting list (this is why your attempt to use Cast<double[][]>failed). Cast<double[]> yields an IEnumerable<double[]>.
To convert this IEnumerable<double[]> to an array of double[] (i.e., a double[][]), we can use LINQ's ToArray().

Note that this will

create a new outer array (i.e., object.ReferenceEquals(a, b) is false), but
the new outer array will reference the same inner arrays (i.e., object.ReferenceEquals(a[0], b[0]) is true).

answered Jan 23, 2023 at 12:43

Heinzi

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Comments

Vivek Nuna · Accepted Answer · 2023-01-23 12:44:35Z

2

You can use LINQ double[][] b = a.Select(x => (double[])x).ToArray();

another way is to use Array.ConvertAll method, It takes a callback function which is called for each element in the given array.

double[][] b = Array.ConvertAll(a, x => (double[])x);

answered Jan 23, 2023 at 12:44

Vivek Nuna

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