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Fits an ordinal encoder on a row-major matrix of categories.

public static OrdinalEncoder<T> Ordinal<T>(ReadOnlySpan<T> values, int featureCount) where T : IComparable<T>, IEquatable<T>

Type parameters — T is the category type; string and int are the two the reference takes.

Parameters — values is the categories, row-major: featureCount per row. featureCount is how many values each row carries.

Returns — a fitted OrdinalEncoder<T>.

Exceptions — ArgumentOutOfRangeException when featureCount is not positive. ArgumentException when values holds no row, a partial one, or a null.

Example — integers encode by their rank among the distinct values, not by their own magnitude.

using Lodestar.Preprocessing;

int[] values = [10, 2, 33, 2];

OrdinalEncoder<int> encoder = Encoders.Ordinal(values, featureCount: 1);

string codes = string.Join(",", encoder.Transform(values));  // => 1,0,2,0

Remarks — no options: the reference's handle_unknown="use_encoded_value" needs a value outside the codes, and nothing here asks for one yet — an unseen category is refused, which is the reference's own default.

Applies to — net10.0, netstandard2.0.

See also — OrdinalEncoder, Encoders.OneHot.