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SentencePiece

One piece of a SentencePiece vocabulary: its text, its score, its id.

public readonly record struct SentencePiece

Properties — Piece is the token text, Score its log probability, Id its id.

Example — the four pieces of a tiny vocabulary.

using Lodestar.Embeddings.Tokenization;

var piece = new SentencePiece("▁alpha", -1.5, 2);

string text = piece.Piece;  // => ▁alpha
double score = piece.Score;  // => -1.5

Remarks — the leading ▁ (U+2581, not an underscore) is part of the token, and it means "a space came before this". That is what lets SentencePiece work with no pre-tokenizer: the word boundary is inside the vocabulary rather than assumed by a regex, so a language written without spaces tokenizes the same way as one written with them.

Score is what the unigram algorithm maximises: encoding picks the segmentation whose scores sum highest, which is why a lower-scoring piece can still be chosen when it enables a better whole. It is a log probability, so it is negative and closer to zero is more likely.

A readonly record struct, so it is copied rather than referenced and compares by value.

Applies to — net10.0, netstandard2.0.

See also — SentencePieceVocabulary, SentencePieceType.