https://github.com/rob-blackbourn/jetblack.arrayindexing

Multi dimensional indexing of one dimensional arrays in C#
https://github.com/rob-blackbourn/jetblack.arrayindexing

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Multi dimensional indexing of one dimensional arrays in C#

• Host: GitHub
• URL: https://github.com/rob-blackbourn/jetblack.arrayindexing
• Owner: rob-blackbourn
• License: mit
• Created: 2015-05-15T10:25:21.000Z (over 9 years ago)
• Default Branch: master
• Last Pushed: 2015-05-15T10:41:13.000Z (over 9 years ago)
• Last Synced: 2024-03-15T00:56:04.658Z (8 months ago)
• Language: C#
• Homepage:
• Size: 133 KB
• Stars: 0
• Watchers: 2
• Forks: 0
• Open Issues: 0
• Metadata Files:
  • Readme: README.md
  • License: License.txt

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README

        
# JetBlack.ArrayIndexing

# Use Case

I had a task where I was presented with a large one-dimensional array, which

represented an n-dimensional matrix. I wanted to be able to index into the

matrix without rebuilding it as multi-dimensional.

# Example

The following test demonstates the behaviour.

```cs

    var array3D = new IndexableArray(

        new[]

        {

            0, 1, 2, 3,

            4, 5, 6, 7,

            8, 9, 10, 11,

            12, 13, 14, 15,

            16, 17, 18, 19,

            20, 21, 22, 23

        },

        4, 3, 2);

    Assert.AreEqual(0, array3D[0, 0, 0]);

    Assert.AreEqual(20, array3D[0, 2, 1]);

    Assert.AreEqual(23, array3D[3, 2, 1]);

```

# Algorithm

The following algorithm is used to transform the n-dimensional indices into a 1-dimensional index.

```cs

    public int ToIndex(int[] bounds, params int[] indices)

    {

        var index = indices[0];

        for (int i = 1, sum = bounds[i - 1]; i < indices.Length; ++i, sum *= bounds[i - 1])

            index += sum * indices[i];

        return index;

    }

```

It should be clear that the sum of the bounds at each dimension can be

precomputed. The `ArrayIndexer` class does this optimisation.