tf.contrib.lookup.IdTableWithHashBuckets

String to Id table wrapper that assigns out-of-vocabulary keys to buckets.

Inherits From: LookupInterface

tf.contrib.lookup.IdTableWithHashBuckets(
    table, num_oov_buckets, hasher_spec=tf.contrib.lookup.FastHashSpec, name=None,
    key_dtype=None
)

For example, if an instance of IdTableWithHashBuckets is initialized with a string-to-id table that maps:

• emerson -> 0
• lake -> 1
• palmer -> 2

The IdTableWithHashBuckets object will performs the following mapping:

• emerson -> 0
• lake -> 1
• palmer -> 2
• <other term> -> bucket_id, where bucket_id will be between 3 and 3 + num_oov_buckets - 1, calculated by: hash(<term>) % num_oov_buckets + vocab_size

If input_tensor is ["emerson", "lake", "palmer", "king", "crimson"], the lookup result is [0, 1, 2, 4, 7].

If table is None, only out-of-vocabulary buckets are used.

Example usage:

num_oov_buckets = 3
input_tensor = tf.constant(["emerson", "lake", "palmer", "king", "crimnson"])
table = tf.IdTableWithHashBuckets(
    tf.StaticHashTable(tf.TextFileIdTableInitializer(filename),
                       default_value),
    num_oov_buckets)
out = table.lookup(input_tensor).
table.init.run()
print(out.eval())

The hash function used for generating out-of-vocabulary buckets ID is handled by hasher_spec.

Args
table	Table that maps tf.string or tf.int64 keys to tf.int64 ids.
num_oov_buckets	Number of buckets to use for out-of-vocabulary keys.
hasher_spec	A HasherSpec to specify the hash function to use for assignation of out-of-vocabulary buckets (optional).
name	A name for the operation (optional).
key_dtype	Data type of keys passed to lookup. Defaults to table.key_dtype if table is specified, otherwise tf.string. Must be string or integer, and must be castable to table.key_dtype.

Raises
ValueError	when table in None and num_oov_buckets is not positive.
TypeError	when hasher_spec is invalid.

Attributes
init	DEPRECATED FUNCTION
initializer
key_dtype	The table key dtype.
name	The name of the table.
resource_handle	Returns the resource handle associated with this Resource.
value_dtype	The table value dtype.

Methods

lookup

View source

lookup(
    keys, name=None
)

Looks up keys in the table, outputs the corresponding values.

It assigns out-of-vocabulary keys to buckets based in their hashes.

Args
keys	Keys to look up. May be either a SparseTensor or dense Tensor.
name	Optional name for the op.

Returns
A SparseTensor if keys are sparse, otherwise a dense Tensor.

Raises
TypeError	when keys doesn't match the table key data type.

size

View source

size(
    name=None
)

Compute the number of elements in this table.