Table Of Contents
Table Of Contents

mx.nd.SequenceMask

Description

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.]]]

Arguments

Argument

Description

data

NDArray-or-Symbol n-dimensional input array of the form [max_sequence_length, batch_size, other_feature_dims] where n>2

sequence.length

NDArray-or-Symbol 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.