mxnet.npx.sequence_mask¶
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sequence_mask
(data=None, sequence_length=None, use_sequence_length=_Null, value=_Null, axis=_Null, out=None, name=None, **kwargs)¶ Sets all elements outside the sequence to a constant value.
This function takes an n-dimensional input array of the form [max_sequence_length, batch_size, other_feature_dims] and returns an array of the same shape.
Parameter sequence_length is used to handle variable-length sequences. sequence_length should be an input array of positive ints of dimension [batch_size]. To use this parameter, set use_sequence_length to True, otherwise each example in the batch is assumed to have the max sequence length and this operator works as the identity operator.
Example:
x = [[[ 1., 2., 3.], [ 4., 5., 6.]], [[ 7., 8., 9.], [ 10., 11., 12.]], [[ 13., 14., 15.], [ 16., 17., 18.]]] // Batch 1 B1 = [[ 1., 2., 3.], [ 7., 8., 9.], [ 13., 14., 15.]] // Batch 2 B2 = [[ 4., 5., 6.], [ 10., 11., 12.], [ 16., 17., 18.]] // works as identity operator when sequence_length parameter is not used SequenceMask(x) = [[[ 1., 2., 3.], [ 4., 5., 6.]], [[ 7., 8., 9.], [ 10., 11., 12.]], [[ 13., 14., 15.], [ 16., 17., 18.]]] // sequence_length [1,1] means 1 of each batch will be kept // and other rows are masked with default mask value = 0 SequenceMask(x, sequence_length=[1,1], use_sequence_length=True) = [[[ 1., 2., 3.], [ 4., 5., 6.]], [[ 0., 0., 0.], [ 0., 0., 0.]], [[ 0., 0., 0.], [ 0., 0., 0.]]] // sequence_length [2,3] means 2 of batch B1 and 3 of batch B2 will be kept // and other rows are masked with value = 1 SequenceMask(x, sequence_length=[2,3], use_sequence_length=True, value=1) = [[[ 1., 2., 3.], [ 4., 5., 6.]], [[ 7., 8., 9.], [ 10., 11., 12.]], [[ 1., 1., 1.], [ 16., 17., 18.]]]
Defined in /work/mxnet/src/operator/sequence_mask.cc:L190
- Parameters
data (ndarray) – n-dimensional input array of the form [max_sequence_length, batch_size, other_feature_dims] where n>2
sequence_length (ndarray) – vector of sequence lengths of the form [batch_size]
use_sequence_length (boolean, optional, default=0) – If set to true, this layer takes in an extra input parameter sequence_length to specify variable length sequence
value (float, optional, default=0) – The value to be used as a mask.
axis (int, optional, default='0') – The sequence axis. Only values of 0 and 1 are currently supported.
out (ndarray, optional) – The output ndarray to hold the result.
- Returns
out – The output of this function.
- Return type
ndarray or list of ndarrays