one.util.streamex.DoubleCollector Maven / Gradle / Ivy
/*
* Copyright 2015, 2017 StreamEx contributors
*
* Licensed 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.
*/
package one.util.streamex;
import java.util.DoubleSummaryStatistics;
import java.util.HashMap;
import java.util.Map;
import java.util.Objects;
import java.util.OptionalDouble;
import java.util.function.BiConsumer;
import java.util.function.DoubleFunction;
import java.util.function.DoublePredicate;
import java.util.function.Function;
import java.util.function.DoubleBinaryOperator;
import java.util.function.DoubleUnaryOperator;
import java.util.function.ObjDoubleConsumer;
import java.util.function.Supplier;
import java.util.stream.Collector;
import static one.util.streamex.StreamExInternals.*;
/**
* A {@link Collector} specialized to work with primitive {@code double}.
*
* @author Tagir Valeev
*
* @param the mutable accumulation type of the reduction operation (often
* hidden as an implementation detail)
* @param the result type of the reduction operation
* @see DoubleStreamEx#collect(DoubleCollector)
* @since 0.3.0
*/
public interface DoubleCollector extends MergingCollector {
/**
* A function that folds a value into a mutable result container.
*
* @return a function which folds a value into a mutable result container
*/
ObjDoubleConsumer doubleAccumulator();
/**
* A function that folds a value into a mutable result container.
*
* The default implementation calls {@link #doubleAccumulator()} on unboxed
* value.
*
* @return a function which folds a value into a mutable result container
*/
@Override
default BiConsumer accumulator() {
return doubleAccumulator()::accept;
}
/**
* Adapts this collector to perform an additional finishing transformation.
*
* @param result type of the resulting collector
* @param finisher a function to be applied to the final result of this
* collector
* @return a collector which performs the action of this collector, followed
* by an additional finishing step
* @since 0.3.7
*/
default DoubleCollector andThen(Function finisher) {
return of(supplier(), doubleAccumulator(), merger(), finisher().andThen(finisher));
}
/**
* Returns a new {@code DoubleCollector} described by the given
* {@code supplier}, {@code accumulator}, and {@code merger} functions. The
* resulting {@code DoubleCollector} has the
* {@code Collector.Characteristics.IDENTITY_FINISH} characteristic.
*
* @param supplier The supplier function for the new collector
* @param doubleAccumulator The doubleAccumulator function for the new
* collector
* @param merger The merger function for the new collector
* @param The type of intermediate accumulation result, and final
* result, for the new collector
* @return the new {@code DoubleCollector}
*/
static DoubleCollector of(Supplier supplier, ObjDoubleConsumer doubleAccumulator,
BiConsumer merger) {
return new DoubleCollectorImpl<>(supplier, doubleAccumulator, merger, Function.identity(), ID_CHARACTERISTICS);
}
/**
* Adapts a {@code Collector} which accepts elements of type {@code Double}
* to a {@code DoubleCollector}.
*
* @param The intermediate accumulation type of the collector
* @param The final result type of the collector
* @param collector a {@code Collector} to adapt
* @return a {@code DoubleCollector} which behaves in the same way as input
* collector.
*/
static DoubleCollector of(Collector collector) {
if (collector instanceof DoubleCollector) {
return (DoubleCollector) collector;
}
return mappingToObj(Double::valueOf, collector);
}
/**
* Returns a new {@code DoubleCollector} described by the given
* {@code supplier}, {@code accumulator}, {@code merger}, and
* {@code finisher} functions.
*
* @param supplier The supplier function for the new collector
* @param doubleAccumulator The doubleAccumulator function for the new
* collector
* @param merger The merger function for the new collector
* @param finisher The finisher function for the new collector
* @param The intermediate accumulation type of the new collector
* @param The final result type of the new collector
* @return the new {@code DoubleCollector}
*/
static DoubleCollector of(Supplier supplier, ObjDoubleConsumer doubleAccumulator,
BiConsumer merger, Function finisher) {
return new DoubleCollectorImpl<>(supplier, doubleAccumulator, merger, finisher, NO_CHARACTERISTICS);
}
/**
* Returns a {@code DoubleCollector} that converts the input numbers to
* strings and concatenates them, separated by the specified delimiter, with
* the specified prefix and suffix, in encounter order.
*
* @param delimiter the delimiter to be used between each element
* @param prefix the sequence of characters to be used at the beginning of
* the joined result
* @param suffix the sequence of characters to be used at the end of the
* joined result
* @return A {@code DoubleCollector} which concatenates the input numbers,
* separated by the specified delimiter, in encounter order
*/
static DoubleCollector joining(CharSequence delimiter, CharSequence prefix, CharSequence suffix) {
return PartialCollector.joining(delimiter, prefix, suffix, true).asDouble(
StreamExInternals.joinAccumulatorDouble(delimiter));
}
/**
* Returns a {@code DoubleCollector} that converts the input numbers to
* strings and concatenates them, separated by the specified delimiter, in
* encounter order.
*
* @param delimiter the delimiter to be used between each element
* @return A {@code DoubleCollector} which concatenates the input numbers,
* separated by the specified delimiter, in encounter order
*/
static DoubleCollector joining(CharSequence delimiter) {
return PartialCollector.joining(delimiter, null, null, false).asDouble(
StreamExInternals.joinAccumulatorDouble(delimiter));
}
/**
* Returns a {@code DoubleCollector} that counts the number of input
* elements and returns the result as {@code Long}. If no elements are
* present, the result is 0.
*
* @return a {@code DoubleCollector} that counts the input elements
*/
static DoubleCollector counting() {
return PartialCollector.longSum().asDouble((box, i) -> box[0]++);
}
/**
* Returns an {@code DoubleCollector} that counts the number of input
* elements and returns the result as {@code Integer}. If no elements are
* present, the result is 0.
*
* @return an {@code DoubleCollector} that counts the input elements
*/
static DoubleCollector countingInt() {
return PartialCollector.intSum().asDouble((box, i) -> box[0]++);
}
/**
* Returns a {@code DoubleCollector} that produces the sum of the input
* elements. If no elements are present, the result is 0.0.
*
* @return a {@code DoubleCollector} that produces the sum of the input
* elements
*/
static DoubleCollector summing() {
// Using DoubleSummaryStatistics as Kahan algorithm is implemented there
return summarizing().andThen(DoubleSummaryStatistics::getSum);
}
/**
* Returns a {@code DoubleCollector} that produces the arithmetic mean of
* the input elements or an empty optional if no elements are collected.
*
* @return a {@code DoubleCollector} that produces the arithmetic mean of
* the input elements
* @since 0.3.7
*/
static DoubleCollector averaging() {
return summarizing().andThen(
dss -> dss.getCount() == 0L ? OptionalDouble.empty() : OptionalDouble.of(dss.getAverage()));
}
/**
* Returns a {@code DoubleCollector} that produces the minimal element,
* described as an {@link OptionalDouble}. If no elements are present, the
* result is an empty {@code OptionalDouble}.
*
* @return a {@code DoubleCollector} that produces the minimal element.
*/
static DoubleCollector min() {
return reducing(Double::min);
}
/**
* Returns a {@code DoubleCollector} that produces the maximal element,
* described as an {@link OptionalDouble}. If no elements are present, the
* result is an empty {@code OptionalDouble}.
*
* @return a {@code DoubleCollector} that produces the maximal element.
*/
static DoubleCollector max() {
return reducing(Double::max);
}
/**
* Adapts a {@code DoubleCollector} to another one by applying a mapping
* function to each input element before accumulation.
*
* @param intermediate accumulation type of the downstream collector
* @param result type of collector
* @param mapper a function to be applied to the input elements
* @param downstream a collector which will accept mapped values
* @return a collector which applies the mapping function to the input
* elements and provides the mapped results to the downstream
* collector
*/
static DoubleCollector mapping(DoubleUnaryOperator mapper, DoubleCollector downstream) {
ObjDoubleConsumer downstreamAccumulator = downstream.doubleAccumulator();
return new DoubleCollectorImpl<>(downstream.supplier(), (r, t) -> downstreamAccumulator.accept(r, mapper
.applyAsDouble(t)), downstream.merger(), downstream.finisher(), downstream.characteristics());
}
/**
* Adapts a {@link Collector} accepting elements of type {@code U} to a
* {@code DoubleCollector} by applying a mapping function to each input
* element before accumulation.
*
* @param type of elements accepted by downstream collector
* @param intermediate accumulation type of the downstream collector
* @param result type of collector
* @param mapper a function to be applied to the input elements
* @param downstream a collector which will accept mapped values
* @return a collector which applies the mapping function to the input
* elements and provides the mapped results to the downstream
* collector
*/
static DoubleCollector mappingToObj(DoubleFunction mapper, Collector downstream) {
BiConsumer accumulator = downstream.accumulator();
if (downstream instanceof MergingCollector) {
return new DoubleCollectorImpl<>(downstream.supplier(), (acc, i) -> accumulator
.accept(acc, mapper.apply(i)), ((MergingCollector) downstream).merger(), downstream
.finisher(), downstream.characteristics());
}
return Box.partialCollector(downstream).asDouble((box, i) -> accumulator.accept(box.a, mapper.apply(i)));
}
/**
* Returns a {@code DoubleCollector} which performs a reduction of its input
* numbers under a specified {@link DoubleBinaryOperator}. The result is
* described as an {@link OptionalDouble}.
*
* @param op a {@code DoubleBinaryOperator} used to reduce the input numbers
* @return a {@code DoubleCollector} which implements the reduction
* operation.
*/
static DoubleCollector reducing(DoubleBinaryOperator op) {
return of(PrimitiveBox::new, (box, d) -> {
if (!box.b) {
box.b = true;
box.d = d;
} else {
box.d = op.applyAsDouble(box.d, d);
}
}, (box1, box2) -> {
if (box2.b) {
if (!box1.b) {
box1.from(box2);
} else {
box1.d = op.applyAsDouble(box1.d, box2.d);
}
}
}, PrimitiveBox::asDouble);
}
/**
* Returns a {@code DoubleCollector} which performs a reduction of its input
* numbers under a specified {@code IntBinaryOperator} using the provided
* identity.
*
* @param identity the identity value for the reduction (also, the value
* that is returned when there are no input elements)
* @param op a {@code DoubleBinaryOperator} used to reduce the input numbers
* @return a {@code DoubleCollector} which implements the reduction
* operation
*/
static DoubleCollector reducing(double identity, DoubleBinaryOperator op) {
return of(() -> new double[] { identity }, (box, i) -> box[0] = op.applyAsDouble(box[0], i),
(box1, box2) -> box1[0] = op.applyAsDouble(box1[0], box2[0]), UNBOX_DOUBLE);
}
/**
* Returns a {@code DoubleCollector} which returns summary statistics for
* the input elements.
*
* @return a {@code DoubleCollector} implementing the summary-statistics
* reduction
*/
static DoubleCollector summarizing() {
return of(DoubleSummaryStatistics::new, DoubleSummaryStatistics::accept, DoubleSummaryStatistics::combine);
}
/**
* Returns a {@code DoubleCollector} which partitions the input elements
* according to a {@code DoublePredicate}, and organizes them into a
* {@code Map}.
*
* There are no guarantees on the type, mutability, serializability, or
* thread-safety of the {@code Map} returned.
*
* @param predicate a predicate used for classifying input elements
* @return a {@code DoubleCollector} implementing the partitioning operation
*/
static DoubleCollector> partitioningBy(DoublePredicate predicate) {
return partitioningBy(predicate, toArray());
}
/**
* Returns a {@code DoubleCollector} which partitions the input numbers
* according to a {@code DoublePredicate}, reduces the values in each
* partition according to another {@code IntCollector}, and organizes them
* into a {@code Map} whose values are the result of the
* downstream reduction.
*
*
* There are no guarantees on the type, mutability, serializability, or
* thread-safety of the {@code Map} returned.
*
* @param the intermediate accumulation type of the downstream collector
* @param the result type of the downstream reduction
* @param predicate a predicate used for classifying input elements
* @param downstream a {@code DoubleCollector} implementing the downstream
* reduction
* @return a {@code DoubleCollector} implementing the cascaded partitioning
* operation
*/
static DoubleCollector> partitioningBy(DoublePredicate predicate,
DoubleCollector downstream) {
ObjDoubleConsumer downstreamAccumulator = downstream.doubleAccumulator();
ObjDoubleConsumer> accumulator = (result, t) -> downstreamAccumulator.accept(
predicate.test(t) ? result.trueValue : result.falseValue, t);
return BooleanMap.partialCollector(downstream).asDouble(accumulator);
}
/**
* Returns a {@code DoubleCollector} implementing a "group by" operation on
* input numbers, grouping them according to a classification function, and
* returning the results in a {@code Map}.
*
*
* The classification function maps elements to some key type {@code K}. The
* collector produces a {@code Map} whose keys are the values
* resulting from applying the classification function to the input numbers,
* and whose corresponding values are arrays containing the input numbers
* which map to the associated key under the classification function.
*
*
* There are no guarantees on the type, mutability, serializability, or
* thread-safety of the {@code Map} objects returned.
*
* @param the type of the keys
* @param classifier the classifier function mapping input elements to keys
* @return a {@code DoubleCollector} implementing the group-by operation
*/
static DoubleCollector> groupingBy(DoubleFunction classifier) {
return groupingBy(classifier, toArray());
}
/**
* Returns a {@code DoubleCollector} implementing a cascaded "group by"
* operation on input numbers, grouping them according to a classification
* function, and then performing a reduction operation on the values
* associated with a given key using the specified downstream
* {@code IntCollector}.
*
*
* The classification function maps elements to some key type {@code K}. The
* downstream collector produces a result of type {@code D}. The resulting
* collector produces a {@code Map}.
*
*
* There are no guarantees on the type, mutability, serializability, or
* thread-safety of the {@code Map} returned.
*
* @param the type of the keys
* @param the intermediate accumulation type of the downstream collector
* @param the result type of the downstream reduction
* @param classifier a classifier function mapping input elements to keys
* @param downstream a {@code DoubleCollector} implementing the downstream
* reduction
* @return a {@code DoubleCollector} implementing the cascaded group-by
* operation
*/
static DoubleCollector> groupingBy(DoubleFunction classifier,
DoubleCollector downstream) {
return groupingBy(classifier, HashMap::new, downstream);
}
/**
* Returns a {@code DoubleCollector} implementing a cascaded "group by"
* operation on input numbers, grouping them according to a classification
* function, and then performing a reduction operation on the values
* associated with a given key using the specified downstream
* {@code IntCollector}. The {@code Map} produced by the Collector is
* created with the supplied factory function.
*
*
* The classification function maps elements to some key type {@code K}. The
* downstream collector produces a result of type {@code D}. The resulting
* collector produces a {@code Map}.
*
* @param the type of the keys
* @param the intermediate accumulation type of the downstream collector
* @param the result type of the downstream reduction
* @param the type of the resulting {@code Map}
* @param classifier a classifier function mapping input elements to keys
* @param downstream a {@code DoubleCollector} implementing the downstream
* reduction
* @param mapFactory a function which, when called, produces a new empty
* {@code Map} of the desired type
* @return a {@code DoubleCollector} implementing the cascaded group-by
* operation
*/
static > DoubleCollector groupingBy(DoubleFunction classifier,
Supplier mapFactory, DoubleCollector downstream) {
Supplier downstreamSupplier = downstream.supplier();
Function supplier = k -> downstreamSupplier.get();
ObjDoubleConsumer downstreamAccumulator = downstream.doubleAccumulator();
ObjDoubleConsumer> accumulator = (m, t) -> {
K key = Objects.requireNonNull(classifier.apply(t));
A container = m.computeIfAbsent(key, supplier);
downstreamAccumulator.accept(container, t);
};
return PartialCollector.grouping(mapFactory, downstream).asDouble(accumulator);
}
/**
* Returns a {@code DoubleCollector} that produces the array of the input
* elements. If no elements are present, the result is an empty array.
*
* @return a {@code DoubleCollector} that produces the array of the input
* elements
*/
static DoubleCollector toArray() {
return of(DoubleBuffer::new, DoubleBuffer::add, DoubleBuffer::addAll, DoubleBuffer::toArray);
}
/**
* Returns a {@code DoubleCollector} that produces the {@code float[]} array
* of the input elements converting them via {@code (float)} casting. If no
* elements are present, the result is an empty array.
*
* @return a {@code DoubleCollector} that produces the {@code float[]} array
* of the input elements
*/
static DoubleCollector toFloatArray() {
return of(FloatBuffer::new, FloatBuffer::add, FloatBuffer::addAll, FloatBuffer::toArray);
}
/**
* Returns a {@code DoubleCollector} which produces a boolean array
* containing the results of applying the given predicate to the input
* elements, in encounter order.
*
* @param predicate a non-interfering, stateless predicate to apply to each
* input element. The result values of this predicate are collected
* to the resulting boolean array.
* @return a {@code DoubleCollector} which collects the results of the
* predicate function to the boolean array, in encounter order.
* @since 0.3.8
*/
static DoubleCollector toBooleanArray(DoublePredicate predicate) {
return PartialCollector.booleanArray().asDouble((box, t) -> {
if (predicate.test(t))
box.a.set(box.b);
box.b = StrictMath.addExact(box.b, 1);
});
}
}