Defined in tensorflow/contrib/lookup/

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 string mapping 1-D tensor where each element is a key and corresponding index within the tensor is the value.

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 [mapping size, mapping size + num_oov_buckets - 1].

The underlying table must be initialized by calling or once.

Elements in mapping cannot have duplicates, otherwise when executing the table initializer op, it will throw a FailedPreconditionError.

Sample Usages:

mapping_strings = tf.constant(["emerson", "lake", "palmer"])
table = tf.contrib.lookup.index_table_from_tensor(
    mapping=mapping_strings, num_oov_buckets=1, default_value=-1)
features = tf.constant(["emerson", "lake", "and", "palmer"])
ids = table.lookup(features)

ids.eval()  ==> [0, 1, 4, 2]


  • mapping: A 1-D Tensor that specifies the mapping of keys to indices. The type of this object must be castable to dtype.
  • num_oov_buckets: The number of out-of-vocabulary buckets.
  • 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 assignment of out-of-vocabulary buckets.
  • dtype: The type of values passed to lookup. Only string and integers are supported.
  • name: A name for this op (optional).


The lookup table to map an input Tensor to index int64 Tensor.


  • ValueError: If mapping is invalid.
  • ValueError: If num_oov_buckets is negative.