Source code for apache_beam.transforms.combiners

#
# Licensed to the Apache Software Foundation (ASF) under one or more
# contributor license agreements.  See the NOTICE file distributed with
# this work for additional information regarding copyright ownership.
# The ASF licenses this file to You under the Apache License, Version 2.0
# (the "License"); you may not use this file except in compliance with
# the License.  You may obtain a copy of the License at
#
#    http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
#

"""A library of basic combiner PTransform subclasses."""

from __future__ import absolute_import
from __future__ import division

import heapq
import operator
import random
from builtins import object
from builtins import zip
from functools import cmp_to_key

from past.builtins import long

from apache_beam.transforms import core
from apache_beam.transforms import cy_combiners
from apache_beam.transforms import ptransform
from apache_beam.transforms import window
from apache_beam.transforms.display import DisplayDataItem
from apache_beam.typehints import KV
from apache_beam.typehints import Any
from apache_beam.typehints import Dict
from apache_beam.typehints import Iterable
from apache_beam.typehints import List
from apache_beam.typehints import Tuple
from apache_beam.typehints import TypeVariable
from apache_beam.typehints import Union
from apache_beam.typehints import with_input_types
from apache_beam.typehints import with_output_types

__all__ = [
    'Count',
    'Mean',
    'Sample',
    'Top',
    'ToDict',
    'ToList',
    ]

# Type variables
T = TypeVariable('T')
K = TypeVariable('K')
V = TypeVariable('V')


[docs]class Mean(object): """Combiners for computing arithmetic means of elements."""
[docs] class Globally(ptransform.PTransform): """combiners.Mean.Globally computes the arithmetic mean of the elements."""
[docs] def expand(self, pcoll): return pcoll | core.CombineGlobally(MeanCombineFn())
[docs] class PerKey(ptransform.PTransform): """combiners.Mean.PerKey finds the means of the values for each key."""
[docs] def expand(self, pcoll): return pcoll | core.CombinePerKey(MeanCombineFn())
# TODO(laolu): This type signature is overly restrictive. This should be # more general. @with_input_types(Union[float, int, long]) @with_output_types(float) class MeanCombineFn(core.CombineFn): """CombineFn for computing an arithmetic mean.""" def create_accumulator(self): return (0, 0) def add_input(self, sum_count, element): (sum_, count) = sum_count return sum_ + element, count + 1 def merge_accumulators(self, accumulators): sums, counts = zip(*accumulators) return sum(sums), sum(counts) def extract_output(self, sum_count): (sum_, count) = sum_count if count == 0: return float('NaN') return sum_ / float(count) def for_input_type(self, input_type): if input_type is int: return cy_combiners.MeanInt64Fn() elif input_type is float: return cy_combiners.MeanFloatFn() return self
[docs]class Count(object): """Combiners for counting elements."""
[docs] class Globally(ptransform.PTransform): """combiners.Count.Globally counts the total number of elements."""
[docs] def expand(self, pcoll): return pcoll | core.CombineGlobally(CountCombineFn())
[docs] class PerKey(ptransform.PTransform): """combiners.Count.PerKey counts how many elements each unique key has."""
[docs] def expand(self, pcoll): return pcoll | core.CombinePerKey(CountCombineFn())
[docs] class PerElement(ptransform.PTransform): """combiners.Count.PerElement counts how many times each element occurs."""
[docs] def expand(self, pcoll): paired_with_void_type = KV[pcoll.element_type, Any] return (pcoll | ('%s:PairWithVoid' % self.label >> core.Map(lambda x: (x, None)) .with_output_types(paired_with_void_type)) | core.CombinePerKey(CountCombineFn()))
@with_input_types(Any) @with_output_types(int) class CountCombineFn(core.CombineFn): """CombineFn for computing PCollection size.""" def create_accumulator(self): return 0 def add_input(self, accumulator, element): return accumulator + 1 def add_inputs(self, accumulator, elements): return accumulator + len(list(elements)) def merge_accumulators(self, accumulators): return sum(accumulators) def extract_output(self, accumulator): return accumulator
[docs]class Top(object): """Combiners for obtaining extremal elements.""" # pylint: disable=no-self-argument
[docs] class Of(ptransform.PTransform): """Obtain a list of the compare-most N elements in a PCollection. This transform will retrieve the n greatest elements in the PCollection to which it is applied, where "greatest" is determined by the comparator function supplied as the compare argument. """ def __init__(self, n, compare=None, *args, **kwargs): """Initializer. compare should be an implementation of "a < b" taking at least two arguments (a and b). Additional arguments and side inputs specified in the apply call become additional arguments to the comparator. Defaults to the natural ordering of the elements. The arguments 'key' and 'reverse' may instead be passed as keyword arguments, and have the same meaning as for Python's sort functions. Args: pcoll: PCollection to process. n: number of elements to extract from pcoll. compare: as described above. *args: as described above. **kwargs: as described above. """ self._n = n self._compare = compare self._key = kwargs.pop('key', None) self._reverse = kwargs.pop('reverse', False) self._args = args self._kwargs = kwargs
[docs] def default_label(self): return 'Top(%d)' % self._n
[docs] def expand(self, pcoll): compare = self._compare if (not self._args and not self._kwargs and not self._key and pcoll.windowing.is_default()): if self._reverse: if compare is None or compare is operator.lt: compare = operator.gt else: original_compare = compare compare = lambda a, b: original_compare(b, a) # This is a more efficient global algorithm. top_per_bundle = pcoll | core.ParDo(_TopPerBundle(self._n, compare)) # If pcoll is empty, we can't guerentee that top_per_bundle # won't be empty, so inject at least one empty accumulator # so that downstream is guerenteed to produce non-empty output. empty_bundle = pcoll.pipeline | core.Create([(None, [])]) return ( (top_per_bundle, empty_bundle) | core.Flatten() | core.GroupByKey() | core.ParDo(_MergeTopPerBundle(self._n, compare))) else: return pcoll | core.CombineGlobally( TopCombineFn(self._n, compare, self._key, self._reverse), *self._args, **self._kwargs)
[docs] class PerKey(ptransform.PTransform): """Identifies the compare-most N elements associated with each key. This transform will produce a PCollection mapping unique keys in the input PCollection to the n greatest elements with which they are associated, where "greatest" is determined by the comparator function supplied as the compare argument in the initializer. """ def __init__(self, n, compare=None, *args, **kwargs): """Initializer. compare should be an implementation of "a < b" taking at least two arguments (a and b). Additional arguments and side inputs specified in the apply call become additional arguments to the comparator. Defaults to the natural ordering of the elements. The arguments 'key' and 'reverse' may instead be passed as keyword arguments, and have the same meaning as for Python's sort functions. Args: n: number of elements to extract from input. compare: as described above. *args: as described above. **kwargs: as described above. """ self._n = n self._compare = compare self._key = kwargs.pop('key', None) self._reverse = kwargs.pop('reverse', False) self._args = args self._kwargs = kwargs
[docs] def default_label(self): return 'TopPerKey(%d)' % self._n
[docs] def expand(self, pcoll): """Expands the transform. Raises TypeCheckError: If the output type of the input PCollection is not compatible with KV[A, B]. Args: pcoll: PCollection to process Returns: the PCollection containing the result. """ return pcoll | core.CombinePerKey( TopCombineFn(self._n, self._compare, self._key, self._reverse), *self._args, **self._kwargs)
@staticmethod @ptransform.ptransform_fn def Largest(pcoll, n): """Obtain a list of the greatest N elements in a PCollection.""" return pcoll | Top.Of(n) @staticmethod @ptransform.ptransform_fn def Smallest(pcoll, n): """Obtain a list of the least N elements in a PCollection.""" return pcoll | Top.Of(n, reverse=True) @staticmethod @ptransform.ptransform_fn def LargestPerKey(pcoll, n): """Identifies the N greatest elements associated with each key.""" return pcoll | Top.PerKey(n) @staticmethod @ptransform.ptransform_fn def SmallestPerKey(pcoll, n, reverse=True): """Identifies the N least elements associated with each key.""" return pcoll | Top.PerKey(n, reverse=True)
class _ComparableValue(object): __slots__ = ('value', 'less_than') def __init__(self, value, less_than): self.value = value self.less_than = less_than def __lt__(self, other): return self.less_than(self.value, other.value) def __repr__(self): return "_ComparableValue[%s]" % self.value @with_input_types(T) @with_output_types(KV[None, List[T]]) class _TopPerBundle(core.DoFn): def __init__(self, n, less_than): self._n = n self._less_than = None if less_than is operator.le else less_than def start_bundle(self): self._heap = [] def process(self, element): if self._less_than is not None: element = _ComparableValue(element, self._less_than) if len(self._heap) < self._n: heapq.heappush(self._heap, element) else: heapq.heappushpop(self._heap, element) def finish_bundle(self): # Though sorting here results in more total work, this allows us to # skip most elements in the reducer. # Essentially, given s map bundles, we are trading about O(sn) compares in # the (single) reducer for O(sn log n) compares across all mappers. self._heap.sort() # Unwrap to avoid serialization via pickle. if self._less_than: yield window.GlobalWindows.windowed_value( (None, [wrapper.value for wrapper in self._heap])) else: yield window.GlobalWindows.windowed_value( (None, self._heap)) @with_input_types(KV[None, Iterable[List[T]]]) @with_output_types(List[T]) class _MergeTopPerBundle(core.DoFn): def __init__(self, n, less_than): self._n = n self._less_than = None if less_than is operator.le else less_than def process(self, key_and_bundles): _, bundles = key_and_bundles heap = [] for bundle in bundles: if not heap: if self._less_than: heap = [ _ComparableValue(element, self._less_than) for element in bundle] else: heap = bundle continue for element in reversed(bundle): if self._less_than is not None: element = _ComparableValue(element, self._less_than) if len(heap) < self._n: heapq.heappush(heap, element) elif element <= heap[0]: # Because _TopPerBundle returns sorted lists, all other elements # will also be smaller. break else: heapq.heappushpop(heap, element) heap.sort() if self._less_than: yield [wrapper.value for wrapper in reversed(heap)] else: yield heap[::-1] @with_input_types(T) @with_output_types(List[T]) class TopCombineFn(core.CombineFn): """CombineFn doing the combining for all of the Top transforms. This CombineFn uses a key or comparison operator to rank the elements. Args: compare: (optional) an implementation of "a < b" taking at least two arguments (a and b). Additional arguments and side inputs specified in the apply call become additional arguments to the comparator. key: (optional) a mapping of elements to a comparable key, similar to the key argument of Python's sorting methods. reverse: (optional) whether to order things smallest to largest, rather than largest to smallest """ _MIN_BUFFER_OVERSIZE = 100 _MAX_BUFFER_OVERSIZE = 1000 # TODO(robertwb): Allow taking a key rather than a compare. def __init__(self, n, compare=None, key=None, reverse=False): self._n = n self._buffer_size = max( min(2 * n, n + TopCombineFn._MAX_BUFFER_OVERSIZE), n + TopCombineFn._MIN_BUFFER_OVERSIZE) if compare is operator.lt: compare = None elif compare is operator.gt: compare = None reverse = not reverse if compare: self._compare = ( (lambda a, b, *args, **kwargs: not compare(a, b, *args, **kwargs)) if reverse else compare) else: self._compare = operator.gt if reverse else operator.lt self._key_fn = key self._reverse = reverse def _sort_buffer(self, buffer, lt): if lt in (operator.gt, operator.lt): buffer.sort(key=self._key_fn, reverse=self._reverse) elif self._key_fn: buffer.sort(key=cmp_to_key( (lambda a, b: (not lt(self._key_fn(a), self._key_fn(b))) - (not lt(self._key_fn(b), self._key_fn(a)))))) else: buffer.sort(key=cmp_to_key(lambda a, b: (not lt(a, b)) - (not lt(b, a)))) def display_data(self): return {'n': self._n, 'compare': DisplayDataItem(self._compare.__name__ if hasattr(self._compare, '__name__') else self._compare.__class__.__name__) .drop_if_none()} # The accumulator type is a tuple (threshold, buffer), where threshold # is the smallest element [key] that could possibly be in the top n based # on the elements observed so far, and buffer is a (periodically sorted) # list of candidates of bounded size. def create_accumulator(self, *args, **kwargs): return None, [] def add_input(self, accumulator, element, *args, **kwargs): if args or kwargs: lt = lambda a, b: self._compare(a, b, *args, **kwargs) else: lt = self._compare threshold, buffer = accumulator element_key = self._key_fn(element) if self._key_fn else element if len(buffer) < self._n: if not buffer: return element_key, [element] buffer.append(element) if lt(element_key, threshold): # element_key < threshold return element_key, buffer return accumulator # with mutated buffer elif lt(threshold, element_key): # threshold < element_key buffer.append(element) if len(buffer) < self._buffer_size: return accumulator self._sort_buffer(buffer, lt) min_element = buffer[-self._n] threshold = self._key_fn(min_element) if self._key_fn else min_element return threshold, buffer[-self._n:] return accumulator def merge_accumulators(self, accumulators, *args, **kwargs): accumulators = list(accumulators) if args or kwargs: add_input = lambda accumulator, element: self.add_input( accumulator, element, *args, **kwargs) else: add_input = self.add_input total_accumulator = None for accumulator in accumulators: if total_accumulator is None: total_accumulator = accumulator else: for element in accumulator[1]: total_accumulator = add_input(total_accumulator, element) return total_accumulator def extract_output(self, accumulator, *args, **kwargs): if args or kwargs: lt = lambda a, b: self._compare(a, b, *args, **kwargs) else: lt = self._compare _, buffer = accumulator self._sort_buffer(buffer, lt) return buffer[:-self._n-1:-1] # tail, reversed class Largest(TopCombineFn): def default_label(self): return 'Largest(%s)' % self._n class Smallest(TopCombineFn): def __init__(self, n): super(Smallest, self).__init__(n, reverse=True) def default_label(self): return 'Smallest(%s)' % self._n
[docs]class Sample(object): """Combiners for sampling n elements without replacement.""" # pylint: disable=no-self-argument @staticmethod @ptransform.ptransform_fn def FixedSizeGlobally(pcoll, n): return pcoll | core.CombineGlobally(SampleCombineFn(n)) @staticmethod @ptransform.ptransform_fn def FixedSizePerKey(pcoll, n): return pcoll | core.CombinePerKey(SampleCombineFn(n))
@with_input_types(T) @with_output_types(List[T]) class SampleCombineFn(core.CombineFn): """CombineFn for all Sample transforms.""" def __init__(self, n): super(SampleCombineFn, self).__init__() # Most of this combiner's work is done by a TopCombineFn. We could just # subclass TopCombineFn to make this class, but since sampling is not # really a kind of Top operation, we use a TopCombineFn instance as a # helper instead. self._top_combiner = TopCombineFn(n) def create_accumulator(self): return self._top_combiner.create_accumulator() def add_input(self, heap, element): # Before passing elements to the Top combiner, we pair them with random # numbers. The elements with the n largest random number "keys" will be # selected for the output. return self._top_combiner.add_input(heap, (random.random(), element)) def merge_accumulators(self, heaps): return self._top_combiner.merge_accumulators(heaps) def extract_output(self, heap): # Here we strip off the random number keys we added in add_input. return [e for _, e in self._top_combiner.extract_output(heap)] class _TupleCombineFnBase(core.CombineFn): def __init__(self, *combiners): self._combiners = [core.CombineFn.maybe_from_callable(c) for c in combiners] self._named_combiners = combiners def display_data(self): combiners = [c.__name__ if hasattr(c, '__name__') else c.__class__.__name__ for c in self._named_combiners] return {'combiners': str(combiners)} def create_accumulator(self): return [c.create_accumulator() for c in self._combiners] def merge_accumulators(self, accumulators): return [c.merge_accumulators(a) for c, a in zip(self._combiners, zip(*accumulators))] def extract_output(self, accumulator): return tuple([c.extract_output(a) for c, a in zip(self._combiners, accumulator)]) class TupleCombineFn(_TupleCombineFnBase): """A combiner for combining tuples via a tuple of combiners. Takes as input a tuple of N CombineFns and combines N-tuples by combining the k-th element of each tuple with the k-th CombineFn, outputting a new N-tuple of combined values. """ def add_input(self, accumulator, element): return [c.add_input(a, e) for c, a, e in zip(self._combiners, accumulator, element)] def with_common_input(self): return SingleInputTupleCombineFn(*self._combiners) class SingleInputTupleCombineFn(_TupleCombineFnBase): """A combiner for combining a single value via a tuple of combiners. Takes as input a tuple of N CombineFns and combines elements by applying each CombineFn to each input, producing an N-tuple of the outputs corresponding to each of the N CombineFn's outputs. """ def add_input(self, accumulator, element): return [c.add_input(a, element) for c, a in zip(self._combiners, accumulator)]
[docs]class ToList(ptransform.PTransform): """A global CombineFn that condenses a PCollection into a single list.""" def __init__(self, label='ToList'): # pylint: disable=useless-super-delegation super(ToList, self).__init__(label)
[docs] def expand(self, pcoll): return pcoll | self.label >> core.CombineGlobally(ToListCombineFn())
@with_input_types(T) @with_output_types(List[T]) class ToListCombineFn(core.CombineFn): """CombineFn for to_list.""" def create_accumulator(self): return [] def add_input(self, accumulator, element): accumulator.append(element) return accumulator def merge_accumulators(self, accumulators): return sum(accumulators, []) def extract_output(self, accumulator): return accumulator
[docs]class ToDict(ptransform.PTransform): """A global CombineFn that condenses a PCollection into a single dict. PCollections should consist of 2-tuples, notionally (key, value) pairs. If multiple values are associated with the same key, only one of the values will be present in the resulting dict. """ def __init__(self, label='ToDict'): # pylint: disable=useless-super-delegation super(ToDict, self).__init__(label)
[docs] def expand(self, pcoll): return pcoll | self.label >> core.CombineGlobally(ToDictCombineFn())
@with_input_types(Tuple[K, V]) @with_output_types(Dict[K, V]) class ToDictCombineFn(core.CombineFn): """CombineFn for to_dict.""" def create_accumulator(self): return dict() def add_input(self, accumulator, element): key, value = element accumulator[key] = value return accumulator def merge_accumulators(self, accumulators): result = dict() for a in accumulators: result.update(a) return result def extract_output(self, accumulator): return accumulator class _CurriedFn(core.CombineFn): """Wrapped CombineFn with extra arguments.""" def __init__(self, fn, args, kwargs): self.fn = fn self.args = args self.kwargs = kwargs def create_accumulator(self): return self.fn.create_accumulator(*self.args, **self.kwargs) def add_input(self, accumulator, element): return self.fn.add_input(accumulator, element, *self.args, **self.kwargs) def merge_accumulators(self, accumulators): return self.fn.merge_accumulators(accumulators, *self.args, **self.kwargs) def extract_output(self, accumulator): return self.fn.extract_output(accumulator, *self.args, **self.kwargs) def apply(self, elements): return self.fn.apply(elements, *self.args, **self.kwargs) def curry_combine_fn(fn, args, kwargs): if not args and not kwargs: return fn else: return _CurriedFn(fn, args, kwargs) class PhasedCombineFnExecutor(object): """Executor for phases of combine operations.""" def __init__(self, phase, fn, args, kwargs): self.combine_fn = curry_combine_fn(fn, args, kwargs) if phase == 'all': self.apply = self.full_combine elif phase == 'add': self.apply = self.add_only elif phase == 'merge': self.apply = self.merge_only elif phase == 'extract': self.apply = self.extract_only else: raise ValueError('Unexpected phase: %s' % phase) def full_combine(self, elements): # pylint: disable=invalid-name return self.combine_fn.apply(elements) def add_only(self, elements): # pylint: disable=invalid-name return self.combine_fn.add_inputs( self.combine_fn.create_accumulator(), elements) def merge_only(self, accumulators): # pylint: disable=invalid-name return self.combine_fn.merge_accumulators(accumulators) def extract_only(self, accumulator): # pylint: disable=invalid-name return self.combine_fn.extract_output(accumulator)