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A Dataset
of fixed-length records from one or more binary files.
tf.compat.v2.data.FixedLengthRecordDataset(
filenames, record_bytes, header_bytes=None, footer_bytes=None, buffer_size=None,
compression_type=None, num_parallel_reads=None
)
Args | |
---|---|
filenames
|
A tf.string tensor or tf.data.Dataset containing one or
more filenames.
|
record_bytes
|
A tf.int64 scalar representing the number of bytes in
each record.
|
header_bytes
|
(Optional.) A tf.int64 scalar representing the number of
bytes to skip at the start of a file.
|
footer_bytes
|
(Optional.) A tf.int64 scalar representing the number of
bytes to ignore at the end of a file.
|
buffer_size
|
(Optional.) A tf.int64 scalar representing the number of
bytes to buffer when reading.
|
compression_type
|
(Optional.) A tf.string scalar evaluating to one of
"" (no compression), "ZLIB" , or "GZIP" .
|
num_parallel_reads
|
(Optional.) A tf.int64 scalar representing the
number of files to read in parallel. If greater than one, the records of
files read in parallel are outputted in an interleaved order. If your
input pipeline is I/O bottlenecked, consider setting this parameter to a
value greater than one to parallelize the I/O. If None , files will be
read sequentially.
|
Attributes | |
---|---|
element_spec
|
The type specification of an element of this dataset. |
Methods
apply
apply(
transformation_func
)
Applies a transformation function to this dataset.
apply
enables chaining of custom Dataset
transformations, which are
represented as functions that take one Dataset
argument and return a
transformed Dataset
.
For example:
dataset = (dataset.map(lambda x: x ** 2)
.apply(group_by_window(key_func, reduce_func, window_size))
.map(lambda x: x ** 3))
Args | |
---|---|
transformation_func
|
A function that takes one Dataset argument and
returns a Dataset .
|
Returns | |
---|---|
Dataset
|
The Dataset returned by applying transformation_func to this
dataset.
|
batch
batch(
batch_size, drop_remainder=False
)
Combines consecutive elements of this dataset into batches.
The components of the resulting element will have an additional outer
dimension, which will be batch_size
(or N % batch_size
for the last
element if batch_size
does not divide the number of input elements N
evenly and drop_remainder
is False
). If your program depends on the
batches having the same outer dimension, you should set the drop_remainder
argument to True
to prevent the smaller batch from being produced.
Args | |
---|---|
batch_size
|
A tf.int64 scalar tf.Tensor , representing the number of
consecutive elements of this dataset to combine in a single batch.
|
drop_remainder
|
(Optional.) A tf.bool scalar tf.Tensor , representing
whether the last batch should be dropped in the case it has fewer than
batch_size elements; the default behavior is not to drop the smaller
batch.
|
Returns | |
---|---|
Dataset
|
A Dataset .
|
cache
cache(
filename=''
)
Caches the elements in this dataset.
Args | |
---|---|
filename
|
A tf.string scalar tf.Tensor , representing the name of a
directory on the filesystem to use for caching elements in this Dataset.
If a filename is not provided, the dataset will be cached in memory.
|
Returns | |
---|---|
Dataset
|
A Dataset .
|
concatenate
concatenate(
dataset
)
Creates a Dataset
by concatenating the given dataset with this dataset.
a = Dataset.range(1, 4) # ==> [ 1, 2, 3 ]
b = Dataset.range(4, 8) # ==> [ 4, 5, 6, 7 ]
# The input dataset and dataset to be concatenated should have the same
# nested structures and output types.
# c = Dataset.range(8, 14).batch(2) # ==> [ [8, 9], [10, 11], [12, 13] ]
# d = Dataset.from_tensor_slices([14.0, 15.0, 16.0])
# a.concatenate(c) and a.concatenate(d) would result in error.
a.concatenate(b) # ==> [ 1, 2, 3, 4, 5, 6, 7 ]
Args | |
---|---|
dataset
|
Dataset to be concatenated.
|
Returns | |
---|---|
Dataset
|
A Dataset .
|
enumerate
enumerate(
start=0
)
Enumerates the elements of this dataset.
It is similar to python's enumerate
.
For example:
# NOTE: The following examples use `{ ... }` to represent the
# contents of a dataset.
a = { 1, 2, 3 }
b = { (7, 8), (9, 10) }
# The nested structure of the `datasets` argument determines the
# structure of elements in the resulting dataset.
a.enumerate(start=5)) == { (5, 1), (6, 2), (7, 3) }
b.enumerate() == { (0, (7, 8)), (1, (9, 10)) }
Args | |
---|---|
start
|
A tf.int64 scalar tf.Tensor , representing the start value for
enumeration.
|
Returns | |
---|---|
Dataset
|
A Dataset .
|
filter
filter(
predicate
)
Filters this dataset according to predicate
.
d = tf.data.Dataset.from_tensor_slices([1, 2, 3])
d = d.filter(lambda x: x < 3) # ==> [1, 2]
# `tf.math.equal(x, y)` is required for equality comparison
def filter_fn(x):
return tf.math.equal(x, 1)
d = d.filter(filter_fn) # ==> [1]
Args | |
---|---|
predicate
|
A function mapping a dataset element to a boolean. |
Returns | |
---|---|
Dataset
|
The Dataset containing the elements of this dataset for which
predicate is True .
|
flat_map
flat_map(
map_func
)
Maps map_func
across this dataset and flattens the result.
Use flat_map
if you want to make sure that the order of your dataset
stays the same. For example, to flatten a dataset of batches into a
dataset of their elements:
a = Dataset.from_tensor_slices([ [1, 2, 3], [4, 5, 6], [7, 8, 9] ])
a.flat_map(lambda x: Dataset.from_tensor_slices(x + 1)) # ==>
# [ 2, 3, 4, 5, 6, 7, 8, 9, 10 ]
tf.data.Dataset.interleave()
is a generalization of flat_map
, since
flat_map
produces the same output as
tf.data.Dataset.interleave(cycle_length=1)
Args | |
---|---|
map_func
|
A function mapping a dataset element to a dataset. |
Returns | |
---|---|
Dataset
|
A Dataset .
|
from_generator
@staticmethod
from_generator( generator, output_types, output_shapes=None, args=None )
Creates a Dataset
whose elements are generated by generator
.
The generator
argument must be a callable object that returns
an object that supports the iter()
protocol (e.g. a generator function).
The elements generated by generator
must be compatible with the given
output_types
and (optional) output_shapes
arguments.
For example:
import itertools
tf.compat.v1.enable_eager_execution()
def gen():
for i in itertools.count(1):
yield (i, [1] * i)
ds = tf.data.Dataset.from_generator(
gen, (tf.int64, tf.int64), (tf.TensorShape([]), tf.TensorShape([None])))
for value in ds.take(2):
print value
# (1, array([1]))
# (2, array([1, 1]))
Args | |
---|---|
generator
|
A callable object that returns an object that supports the
iter() protocol. If args is not specified, generator must take no
arguments; otherwise it must take as many arguments as there are values
in args .
|
output_types
|
A nested structure of tf.DType objects corresponding to
each component of an element yielded by generator .
|
output_shapes
|
(Optional.) A nested structure of tf.TensorShape objects
corresponding to each component of an element yielded by generator .
|
args
|
(Optional.) A tuple of tf.Tensor objects that will be evaluated
and passed to generator as NumPy-array arguments.
|
Returns | |
---|---|
Dataset
|
A Dataset .
|
from_tensor_slices
@staticmethod
from_tensor_slices( tensors )
Creates a Dataset
whose elements are slices of the given tensors.
Note that if tensors
contains a NumPy array, and eager execution is not
enabled, the values will be embedded in the graph as one or more
tf.constant
operations. For large datasets (> 1 GB), this can waste
memory and run into byte limits of graph serialization. If tensors
contains one or more large NumPy arrays, consider the alternative described
in this guide.
Args | |
---|---|
tensors
|
A dataset element, with each component having the same size in the 0th dimension. |
Returns | |
---|---|
Dataset
|
A Dataset .
|
from_tensors
@staticmethod
from_tensors( tensors )
Creates a Dataset
with a single element, comprising the given tensors.
Note that if tensors
contains a NumPy array, and eager execution is not
enabled, the values will be embedded in the graph as one or more
tf.constant
operations. For large datasets (> 1 GB), this can waste
memory and run into byte limits of graph serialization. If tensors
contains one or more large NumPy arrays, consider the alternative described
in this
guide.
Args | |
---|---|
tensors
|
A dataset element. |
Returns | |
---|---|
Dataset
|
A Dataset .
|
interleave
interleave(
map_func, cycle_length=AUTOTUNE, block_length=1, num_parallel_calls=None
)
Maps map_func
across this dataset, and interleaves the results.
For example, you can use Dataset.interleave()
to process many input files
concurrently:
# Preprocess 4 files concurrently, and interleave blocks of 16 records from
# each file.
filenames = ["/var/data/file1.txt", "/var/data/file2.txt", ...]
dataset = (Dataset.from_tensor_slices(filenames)
.interleave(lambda x:
TextLineDataset(x).map(parse_fn, num_parallel_calls=1),
cycle_length=4, block_length=16))
The cycle_length
and block_length
arguments control the order in which
elements are produced. cycle_length
controls the number of input elements
that are processed concurrently. If you set cycle_length
to 1, this
transformation will handle one input element at a time, and will produce
identical results to tf.data.Dataset.flat_map
. In general,
this transformation will apply map_func
to cycle_length
input elements,
open iterators on the returned Dataset
objects, and cycle through them
producing block_length
consecutive elements from each iterator, and
consuming the next input element each time it reaches the end of an
iterator.
For example:
a = Dataset.range(1, 6) # ==> [ 1, 2, 3, 4, 5 ]
# NOTE: New lines indicate "block" boundaries.
a.interleave(lambda x: Dataset.from_tensors(x).repeat(6),
cycle_length=2, block_length=4) # ==> [1, 1, 1, 1,
# 2, 2, 2, 2,
# 1, 1,
# 2, 2,
# 3, 3, 3, 3,
# 4, 4, 4, 4,
# 3, 3,
# 4, 4,
# 5, 5, 5, 5,
# 5, 5]
Args | |
---|---|
map_func
|
A function mapping a dataset element to a dataset. |
cycle_length
|
(Optional.) The number of input elements that will be
processed concurrently. If not specified, the value will be derived from
the number of available CPU cores. If the num_parallel_calls argument
is set to tf.data.experimental.AUTOTUNE , the cycle_length argument
also identifies the maximum degree of parallelism.
|
block_length
|
(Optional.) The number of consecutive elements to produce from each input element before cycling to another input element. |
num_parallel_calls
|
(Optional.) If specified, the implementation creates a
threadpool, which is used to fetch inputs from cycle elements
asynchronously and in parallel. The default behavior is to fetch inputs
from cycle elements synchronously with no parallelism. If the value
tf.data.experimental.AUTOTUNE is used, then the number of parallel
calls is set dynamically based on available CPU.
|
Returns | |
---|---|
Dataset
|
A Dataset .
|
list_files
@staticmethod
list_files( file_pattern, shuffle=None, seed=None )
A dataset of all files matching one or more glob patterns.
Example:
If we had the following files on our filesystem:
- /path/to/dir/a.txt
- /path/to/dir/b.py
- /path/to/dir/c.py If we pass "/path/to/dir/*.py" as the directory, the dataset would produce:
- /path/to/dir/b.py
- /path/to/dir/c.py
Args | |
---|---|
file_pattern
|
A string, a list of strings, or a tf.Tensor of string type
(scalar or vector), representing the filename glob (i.e. shell wildcard)
pattern(s) that will be matched.
|
shuffle
|
(Optional.) If True , the file names will be shuffled randomly.
Defaults to True .
|
seed
|
(Optional.) A tf.int64 scalar tf.Tensor , representing the random
seed that will be used to create the distribution. See
tf.compat.v1.set_random_seed for behavior.
|
Returns | |
---|---|
Dataset
|
A Dataset of strings corresponding to file names.
|
map
map(
map_func, num_parallel_calls=None
)
Maps map_func
across the elements of this dataset.
This transformation applies map_func
to each element of this dataset, and
returns a new dataset containing the transformed elements, in the same
order as they appeared in the input.
For example:
a = Dataset.range(1, 6) # ==> [ 1, 2, 3, 4, 5 ]
a.map(lambda x: x + 1) # ==> [ 2, 3, 4, 5, 6 ]
The input signature of map_func
is determined by the structure of each
element in this dataset. For example:
# NOTE: The following examples use `{ ... }` to represent the
# contents of a dataset.
# Each element is a `tf.Tensor` object.
a = { 1, 2, 3, 4, 5 }
# `map_func` takes a single argument of type `tf.Tensor` with the same
# shape and dtype.
result = a.map(lambda x: ...)
# Each element is a tuple containing two `tf.Tensor` objects.
b = { (1, "foo"), (2, "bar"), (3, "baz") }
# `map_func` takes two arguments of type `tf.Tensor`.
result = b.map(lambda x_int, y_str: ...)
# Each element is a dictionary mapping strings to `tf.Tensor` objects.
c = { {"a": 1, "b": "foo"}, {"a": 2, "b": "bar"}, {"a": 3, "b": "baz"} }
# `map_func` takes a single argument of type `dict` with the same keys as
# the elements.
result = c.map(lambda d: ...)
The value or values returned by map_func
determine the structure of each
element in the returned dataset.
# `map_func` returns a scalar `tf.Tensor` of type `tf.float32`.
def f(...):
return tf.constant(37.0)
result = dataset.map(f)
result.output_classes == tf.Tensor
result.output_types == tf.float32
result.output_shapes == [] # scalar
# `map_func` returns two `tf.Tensor` objects.
def g(...):
return tf.constant(37.0), tf.constant(["Foo", "Bar", "Baz"])
result = dataset.map(g)
result.output_classes == (tf.Tensor, tf.Tensor)
result.output_types == (tf.float32, tf.string)
result.output_shapes == ([], [3])
# Python primitives, lists, and NumPy arrays are implicitly converted to
# `tf.Tensor`.
def h(...):
return 37.0, ["Foo", "Bar", "Baz"], np.array([1.0, 2.0] dtype=np.float64)
result = dataset.map(h)
result.output_classes == (tf.Tensor, tf.Tensor, tf.Tensor)
result.output_types == (tf.float32, tf.string, tf.float64)
result.output_shapes == ([], [3], [2])
# `map_func` can return nested structures.
def i(...):
return {"a": 37.0, "b": [42, 16]}, "foo"
result.output_classes == ({"a": tf.Tensor, "b": tf.Tensor}, tf.Tensor)
result.output_types == ({"a": tf.float32, "b": tf.int32}, tf.string)
result.output_shapes == ({"a": [], "b": [2]}, [])
map_func
can accept as arguments and return any type of dataset element.
Note that irrespective of the context in which map_func
is defined (eager
vs. graph), tf.data traces the function and executes it as a graph. To use
Python code inside of the function you have two options:
1) Rely on AutoGraph to convert Python code into an equivalent graph computation. The downside of this approach is that AutoGraph can convert some but not all Python code.
2) Use tf.py_function
, which allows you to write arbitrary Python code but
will generally result in worse performance than 1). For example:
d = tf.data.Dataset.from_tensor_slices(['hello', 'world'])
# transform a string tensor to upper case string using a Python function
def upper_case_fn(t: tf.Tensor) -> str:
return t.numpy().decode('utf-8').upper()
d.map(lambda x: tf.py_function(func=upper_case_fn,
inp=[x], Tout=tf.string)) # ==> [ "HELLO", "WORLD" ]
Args | |
---|---|
map_func
|
A function mapping a dataset element to another dataset element. |
num_parallel_calls
|
(Optional.) A tf.int32 scalar tf.Tensor ,
representing the number elements to process asynchronously in parallel.
If not specified, elements will be processed sequentially. If the value
tf.data.experimental.AUTOTUNE is used, then the number of parallel
calls is set dynamically based on available CPU.
|
Returns | |
---|---|
Dataset
|
A Dataset .
|
options
options()
Returns the options for this dataset and its inputs.
Returns | |
---|---|
A tf.data.Options object representing the dataset options.
|
padded_batch
padded_batch(
batch_size, padded_shapes, padding_values=None, drop_remainder=False
)
Combines consecutive elements of this dataset into padded batches.
This transformation combines multiple consecutive elements of the input dataset into a single element.
Like tf.data.Dataset.batch
, the components of the resulting element will
have an additional outer dimension, which will be batch_size
(or
N % batch_size
for the last element if batch_size
does not divide the
number of input elements N
evenly and drop_remainder
is False
). If
your program depends on the batches having the same outer dimension, you
should set the drop_remainder
argument to True
to prevent the smaller
batch from being produced.
Unlike tf.data.Dataset.batch
, the input elements to be batched may have
different shapes, and this transformation will pad each component to the
respective shape in padding_shapes
. The padding_shapes
argument
determines the resulting shape for each dimension of each component in an
output element:
- If the dimension is a constant (e.g.
tf.compat.v1.Dimension(37)
), the component will be padded out to that length in that dimension. - If the dimension is unknown (e.g.
tf.compat.v1.Dimension(None)
), the component will be padded out to the maximum length of all elements in that dimension.
See also tf.data.experimental.dense_to_sparse_batch
, which combines
elements that may have different shapes into a tf.SparseTensor
.
Args | |
---|---|
batch_size
|
A tf.int64 scalar tf.Tensor , representing the number of
consecutive elements of this dataset to combine in a single batch.
|
padded_shapes
|
A nested structure of tf.TensorShape or tf.int64 vector
tensor-like objects representing the shape to which the respective
component of each input element should be padded prior to batching. Any
unknown dimensions (e.g. tf.compat.v1.Dimension(None) in a
tf.TensorShape or -1 in a tensor-like object) will be padded to the
maximum size of that dimension in each batch.
|
padding_values
|
(Optional.) A nested structure of scalar-shaped
tf.Tensor , representing the padding values to use for the respective
components. Defaults are 0 for numeric types and the empty string for
string types.
|
drop_remainder
|
(Optional.) A tf.bool scalar tf.Tensor , representing
whether the last batch should be dropped in the case it has fewer than
batch_size elements; the default behavior is not to drop the smaller
batch.
|
Returns | |
---|---|
Dataset
|
A Dataset .
|
prefetch
prefetch(
buffer_size
)
Creates a Dataset
that prefetches elements from this dataset.
Args | |
---|---|
buffer_size
|
A tf.int64 scalar tf.Tensor , representing the maximum
number of elements that will be buffered when prefetching.
|
Returns | |
---|---|
Dataset
|
A Dataset .
|
range
@staticmethod
range( *args )
Creates a Dataset
of a step-separated range of values.
For example:
Dataset.range(5) == [0, 1, 2, 3, 4]
Dataset.range(2, 5) == [2, 3, 4]
Dataset.range(1, 5, 2) == [1, 3]
Dataset.range(1, 5, -2) == []
Dataset.range(5, 1) == []
Dataset.range(5, 1, -2) == [5, 3]
Args | |
---|---|
*args
|
follows the same semantics as python's xrange. len(args) == 1 -> start = 0, stop = args[0], step = 1 len(args) == 2 -> start = args[0], stop = args[1], step = 1 len(args) == 3 -> start = args[0], stop = args[1, stop = args[2] |
Returns | |
---|---|
Dataset
|
A RangeDataset .
|
Raises | |
---|---|
ValueError
|
if len(args) == 0. |
reduce
reduce(
initial_state, reduce_func
)
Reduces the input dataset to a single element.
The transformation calls reduce_func
successively on every element of
the input dataset until the dataset is exhausted, aggregating information in
its internal state. The initial_state
argument is used for the initial
state and the final state is returned as the result.
For example:
tf.data.Dataset.range(5).reduce(np.int64(0), lambda x, _: x + 1)
produces5
tf.data.Dataset.range(5).reduce(np.int64(0), lambda x, y: x + y)
produces10
Args | |
---|---|
initial_state
|
An element representing the initial state of the transformation. |
reduce_func
|
A function that maps (old_state, input_element) to
new_state . It must take two arguments and return a new element
The structure of new_state must match the structure of
initial_state .
|
Returns | |
---|---|
A dataset element corresponding to the final state of the transformation. |
repeat
repeat(
count=None
)
Repeats this dataset count
times.
Args | |
---|---|
count
|
(Optional.) A tf.int64 scalar tf.Tensor , representing the
number of times the dataset should be repeated. The default behavior (if
count is None or -1 ) is for the dataset be repeated indefinitely.
|
Returns | |
---|---|
Dataset
|
A Dataset .
|
shard
shard(
num_shards, index
)
Creates a Dataset
that includes only 1/num_shards
of this dataset.
This dataset operator is very useful when running distributed training, as it allows each worker to read a unique subset.
When reading a single input file, you can skip elements as follows:
d = tf.data.TFRecordDataset(input_file)
d = d.shard(num_workers, worker_index)
d = d.repeat(num_epochs)
d = d.shuffle(shuffle_buffer_size)
d = d.map(parser_fn, num_parallel_calls=num_map_threads)
Important caveats:
- Be sure to shard before you use any randomizing operator (such as shuffle).
- Generally it is best if the shard operator is used early in the dataset pipeline. For example, when reading from a set of TFRecord files, shard before converting the dataset to input samples. This avoids reading every file on every worker. The following is an example of an efficient sharding strategy within a complete pipeline:
d = Dataset.list_files(pattern)
d = d.shard(num_workers, worker_index)
d = d.repeat(num_epochs)
d = d.shuffle(shuffle_buffer_size)
d = d.interleave(tf.data.TFRecordDataset,
cycle_length=num_readers, block_length=1)
d = d.map(parser_fn, num_parallel_calls=num_map_threads)
Args | |
---|---|
num_shards
|
A tf.int64 scalar tf.Tensor , representing the number of
shards operating in parallel.
|
index
|
A tf.int64 scalar tf.Tensor , representing the worker index.
|
Returns | |
---|---|
Dataset
|
A Dataset .
|
Raises | |
---|---|
InvalidArgumentError
|
if num_shards or index are illegal values.
Note: error checking is done on a best-effort basis, and errors aren't
guaranteed to be caught upon dataset creation. (e.g. providing in a
placeholder tensor bypasses the early checking, and will instead result
in an error during a session.run call.)
|
shuffle
shuffle(
buffer_size, seed=None, reshuffle_each_iteration=None
)
Randomly shuffles the elements of this dataset.
This dataset fills a buffer with buffer_size
elements, then randomly
samples elements from this buffer, replacing the selected elements with new
elements. For perfect shuffling, a buffer size greater than or equal to the
full size of the dataset is required.
For instance, if your dataset contains 10,000 elements but buffer_size
is
set to 1,000, then shuffle
will initially select a random element from
only the first 1,000 elements in the buffer. Once an element is selected,
its space in the buffer is replaced by the next (i.e. 1,001-st) element,
maintaining the 1,000 element buffer.
Args | |
---|---|
buffer_size
|
A tf.int64 scalar tf.Tensor , representing the number of
el |