liveBook · Manning

Padding token

As explained in Deep Learning with R, Third Edition

A padding token is a placeholder token inserted to make sequences conform to a common length and carries no sequence content.

A padding token is a placeholder inserted after shorter sequences so a batch reaches a shared length without adding sequence content. Models can identify these positions and ignore them during processing. section 14.5.3 section 15.4.3

A padded review

The token sequence c("the", "movie", "was", "awful", "[PAD]", "[PAD]", "[PAD]", "[PAD]") keeps a short review aligned with longer sequences while preserving its actual words.

Padding tokens support several connected preprocessing steps:

  • Pack sequences to a fixed length, appending padding after the meaningful tokens and trimming sequences that exceed the limit. section 15.4.3
  • Return a padding mask alongside token IDs so downstream models can distinguish real tokens from padding positions. section 15.4.3

How Deep Learning with R, Third Edition covers it

How deep it goes
Explains placeholder placement, fixed-length packing, truncation, masking, and framework configuration without detailing mask propagation internals.
Examples
Demonstrates padded movie-review sequences, RoBERTa start-end packing, and batched token IDs paired with Boolean padding masks.
What it assumes
Assumes tokenization and integer token IDs, while demonstrating how padding and its mask enter preprocessing from that point.
What you can do after
Apply it via KerasHub’s StartEndPacker or Keras Embedding masking when preparing variable-length text for neural models.
How it connects
Connects padding tokens to tokenization, token packing, sequence length, padding masks, embeddings, and recurrent or Transformer models.

Also explained in

Compare how 4 books explain padding token →

Related concepts

This explainer was generated by Manning's knowledge graph from the text of Deep Learning with R, Third Edition. The section links point to the parts of the book it draws on.