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.NET: Find the Index Value When Using LINQ Select()

Here is an example of making a one-hot encoding for tasks like classification/categorization in machine learning. It requires the index during the Select() modifier.

var string_array = new string[] { "D", "A", "I", "G", "F", "C", "J", "E", "H", "B" }.OrderBy(x => x).ToArray();
var array_of_arrays = string_array.Select((val, index) =>
{
    var one_hot = new double[string_array.Length];
    one_hot[index] = 1; // NOTE: index used here
    return one_hot;
}).ToArray();

foreach (var str in string_array)
    Console.Write(str + ' ');
Console.WriteLine("\r\n");

foreach (var array in array_of_arrays)
{
    foreach (var dbl in array)
        Console.Write(dbl + " ");
    Console.WriteLine();
}

The above code will output this:

A B C D E F G H I J

1 0 0 0 0 0 0 0 0 0
0 1 0 0 0 0 0 0 0 0
0 0 1 0 0 0 0 0 0 0
0 0 0 1 0 0 0 0 0 0
0 0 0 0 1 0 0 0 0 0
0 0 0 0 0 1 0 0 0 0
0 0 0 0 0 0 1 0 0 0
0 0 0 0 0 0 0 1 0 0
0 0 0 0 0 0 0 0 1 0
0 0 0 0 0 0 0 0 0 1

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