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Generate next tokens after a context and their predictability using a causal transformer model

Source: R/tr_causal.R
causal_next_tokens_pred_tbl.Rd

This function predicts the possible next tokens and their predictability (log-probabilities by default). The function sorts tokens in descending order of their predictability.

Usage

causal_next_tokens_pred_tbl(
  context,
  log.p = getOption("pangoling.log.p"),
  decode = FALSE,
  model = getOption("pangoling.causal.default"),
  checkpoint = NULL,
  add_special_tokens = NULL,
  config_model = NULL,
  config_tokenizer = NULL
)

Arguments

context

A single string representing the context for which the next tokens and their predictabilities are predicted.

log.p

Base of the logarithm used for the output predictability values. If TRUE (default), the natural logarithm (base e) is used. If FALSE, the raw probabilities are returned. Alternatively, log.p can be set to a numeric value specifying the base of the logarithm (e.g., 2 for base-2 logarithms). To get surprisal in bits (rather than predictability), set log.p = 1/2.

decode

Logical. If TRUE, decodes the tokens into human-readable strings, handling special characters and diacritics. Default is FALSE.

model

Name of a pre-trained model or folder. One should be able to use models based on "gpt2". See hugging face website.

checkpoint

Folder of a checkpoint.

add_special_tokens

Whether to include special tokens. It has the same default as the AutoTokenizer method in Python.

config_model

List with other arguments that control how the model from Hugging Face is accessed.

config_tokenizer

List with other arguments that control how the tokenizer from Hugging Face is accessed.

Value

A table with possible next tokens and their log-probabilities.

Details

The function uses a causal transformer model to compute the predictability of all tokens in the model's vocabulary, given a single input context. It returns a table where each row represents a token, along with its predictability score. By default, the function returns log-probabilities in natural logarithm (base e), but you can specify a different logarithm base (e.g., log.p = 1/2 for surprisal in bits).

If decode = TRUE, the tokens are converted into human-readable strings, handling special characters like accents and diacritics. This ensures that tokens are more interpretable, especially for languages with complex tokenization.

More details about causal models

A causal language model (also called GPT-like, auto-regressive, or decoder model) is a type of large language model usually used for text-generation that can predict the next word (or more accurately in fact token) based on a preceding context.

If not specified, the causal model used will be the one set in the global option pangoling.causal.default, this can be accessed via getOption("pangoling.causal.default") (by default "gpt2"). To change the default option use options(pangoling.causal.default = "newcausalmodel").

A list of possible causal models can be found in Hugging Face website.

Using the config_model and config_tokenizer arguments, it's possible to control how the model and tokenizer from Hugging Face is accessed, see the Python method from_pretrained for details.

In case of errors when a new model is run, check the status of https://status.huggingface.co/

See also

Other causal model functions: causal_pred_mats(), causal_words_pred()

Examples

if (FALSE) { # installed_py_pangoling()
causal_next_tokens_pred_tbl(
  context = "The apple doesn't fall far from the",
  model = "gpt2"
)
}