pad_sequences: Pads sequences to the same length.

In keras3: R Interface to 'Keras'

Pads sequences to the same length.

Description

This function transforms a list (of length num_samples) of sequences (lists of integers) into a 2D NumPy array of shape ⁠(num_samples, num_timesteps)⁠. num_timesteps is either the maxlen argument if provided, or the length of the longest sequence in the list.

Sequences that are shorter than num_timesteps are padded with value until they are num_timesteps long.

Sequences longer than num_timesteps are truncated so that they fit the desired length.

The position where padding or truncation happens is determined by the arguments padding and truncating, respectively. Pre-padding or removing values from the beginning of the sequence is the default.

sequence <- list(c(1), c(2, 3), c(4, 5, 6))
pad_sequences(sequence)

##      [,1] [,2] [,3]
## [1,]    0    0    1
## [2,]    0    2    3
## [3,]    4    5    6

pad_sequences(sequence, value=-1)

##      [,1] [,2] [,3]
## [1,]   -1   -1    1
## [2,]   -1    2    3
## [3,]    4    5    6

pad_sequences(sequence, padding='post')

##      [,1] [,2] [,3]
## [1,]    1    0    0
## [2,]    2    3    0
## [3,]    4    5    6

pad_sequences(sequence, maxlen=2)

##      [,1] [,2]
## [1,]    0    1
## [2,]    2    3
## [3,]    5    6

Usage

pad_sequences(
  sequences,
  maxlen = NULL,
  dtype = "int32",
  padding = "pre",
  truncating = "pre",
  value = 0
)

Arguments

sequences	List of sequences (each sequence is a list of integers).
maxlen	Optional Int, maximum length of all sequences. If not provided, sequences will be padded to the length of the longest individual sequence.
dtype	(Optional, defaults to "int32"). Type of the output sequences. To pad sequences with variable length strings, you can use object.
padding	String, "pre" or "post" (optional, defaults to "pre"): pad either before or after each sequence.
truncating	String, "pre" or "post" (optional, defaults to "pre"): remove values from sequences larger than maxlen, either at the beginning or at the end of the sequences.
value	Float or String, padding value. (Optional, defaults to 0)

Value

Array with shape ⁠(len(sequences), maxlen)⁠

See Also

• https://keras.io/api/data_loading/timeseries#padsequences-function

Other utils:
audio_dataset_from_directory()
clear_session()
config_disable_interactive_logging()
config_disable_traceback_filtering()
config_enable_interactive_logging()
config_enable_traceback_filtering()
config_is_interactive_logging_enabled()
config_is_traceback_filtering_enabled()
get_file()
get_source_inputs()
image_array_save()
image_dataset_from_directory()
image_from_array()
image_load()
image_smart_resize()
image_to_array()
layer_feature_space()
normalize()
set_random_seed()
split_dataset()
text_dataset_from_directory()
timeseries_dataset_from_array()
to_categorical()
zip_lists()

keras3 documentation built on June 8, 2025, 1:36 p.m.