util.py

import numpy as np


def pad_sequences(sequences, maxlen=None, dtype='int32', value=0.):
    '''
    Partially borrowed from Keras
    # Arguments
        sequences: list of lists where each element is a sequence
        maxlen: int, maximum length
        dtype: type to cast the resulting sequence.
        value: float, value to pad the sequences to the desired value.
    # Returns
        x: numpy array with dimensions (number_of_sequences, maxlen)
    '''
    lengths = [len(s) for s in sequences]
    nb_samples = len(sequences)
    if maxlen is None:
        maxlen = np.max(lengths)
    # take the sample shape from the first non empty sequence
    # checking for consistency in the main loop below.
    sample_shape = tuple()
    for s in sequences:
        if len(s) > 0:
            sample_shape = np.asarray(s).shape[1:]
            break
    x = (np.ones((nb_samples, maxlen) + sample_shape) * value).astype(dtype)
    for idx, s in enumerate(sequences):
        if len(s) == 0:
            continue  # empty list was found
        # pre truncating
        trunc = s[-maxlen:]
        # check `trunc` has expected shape
        trunc = np.asarray(trunc, dtype=dtype)
        if trunc.shape[1:] != sample_shape:
            raise ValueError('Shape of sample %s of sequence at position %s is different from expected shape %s' %
                             (trunc.shape[1:], idx, sample_shape))
        # post padding
        x[idx, :len(trunc)] = trunc
    return x