tf.contrib.lookup.index_table_from_file

tf.contrib.lookup.index_table_from_file(
    vocabulary_file=None,
    num_oov_buckets=0,
    vocab_size=None,
    default_value=-1,
    hasher_spec=tf.contrib.lookup.FastHashSpec,
    key_dtype=tf.string,
    name=None,
    key_column_index=TextFileIndex.WHOLE_LINE,
    value_column_index=TextFileIndex.LINE_NUMBER,
    delimiter='\t'
)

Defined in tensorflow/python/ops/lookup_ops.py.

Returns a lookup table that converts a string tensor into int64 IDs.

This operation constructs a lookup table to convert tensor of strings into int64 IDs. The mapping can be initialized from a vocabulary file specified in vocabulary_file, where the whole line is the key and the zero-based line number is the ID.

Any lookup of an out-of-vocabulary token will return a bucket ID based on its hash if num_oov_buckets is greater than zero. Otherwise it is assigned the default_value. The bucket ID range is [vocabulary size, vocabulary size + num_oov_buckets - 1].

The underlying table must be initialized by calling tf.tables_initializer.run() or table.init.run() once.

To specify multi-column vocabulary files, use key_column_index and value_column_index and delimiter.

  • TextFileIndex.LINE_NUMBER means use the line number starting from zero, expects data type int64.
  • TextFileIndex.WHOLE_LINE means use the whole line content, expects data type string.
  • A value >=0 means use the index (starting at zero) of the split line based on delimiter.

Sample Usages:

If we have a vocabulary file "test.txt" with the following content:

emerson
lake
palmer
features = tf.constant(["emerson", "lake", "and", "palmer"])
table = tf.lookup.index_table_from_file(
    vocabulary_file="test.txt", num_oov_buckets=1)
ids = table.lookup(features)
...
tf.tables_initializer().run()

ids.eval()  ==> [0, 1, 3, 2]  # where 3 is the out-of-vocabulary bucket

Args:

  • vocabulary_file: The vocabulary filename, may be a constant scalar Tensor.
  • num_oov_buckets: The number of out-of-vocabulary buckets.
  • vocab_size: Number of the elements in the vocabulary, if known.
  • default_value: The value to use for out-of-vocabulary feature values. Defaults to -1.
  • hasher_spec: A HasherSpec to specify the hash function to use for assignation of out-of-vocabulary buckets.
  • key_dtype: The key data type.
  • name: A name for this op (optional).
  • key_column_index: The column index from the text file to get the key values from. The default is to use the whole line content.
  • value_column_index: The column index from the text file to get the value values from. The default is to use the line number, starting from zero.
  • delimiter: The delimiter to separate fields in a line.

Returns:

The lookup table to map a key_dtype Tensor to index int64 Tensor.

Raises:

  • ValueError: If vocabulary_file is not set.
  • ValueError: If num_oov_buckets is negative or vocab_size is not greater than zero.