com.enterprisemath.math.statistics.observation.ListObservationProvider Maven / Gradle / Ivy

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package com.enterprisemath.math.statistics.observation;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.NoSuchElementException;
import java.util.concurrent.atomic.AtomicInteger;

import org.apache.commons.lang3.builder.ToStringBuilder;

import com.enterprisemath.utils.DomainUtils;

/**
 * Provides vector observation from the list in the same order as the source list.
 * It is guaranteed that all the provided vectors have the specified dimension.
 *
 * @author radek.hecl
 *
 * @param  type of the observation
 */
public class ListObservationProvider implements ObservationProvider {

    /**
     * Builder object.
     *
     * @param  type of the observation
     */
    public static class Builder {

        /**
         * Observations.
         */
        private List observations = new ArrayList();

        /**
         * Sets the observations.
         *
         * @param observations observations
         * @return this instance
         */
        public Builder setObservations(List observations) {
            this.observations = DomainUtils.softCopyList(observations);
            return this;
        }

        /**
         * Adds observation into the sequence.
         *
         * @param observation observation
         * @return this instance
         */
        public Builder addObservation(T observation) {
            observations.add(observation);
            return this;
        }

        /**
         * Builds result object.
         *
         * @return created object
         */
        public ListObservationProvider build() {
            return new ListObservationProvider(this);
        }
    }

    /**
     * Observations.
     */
    private List observations = new ArrayList();

    /**
     * Creates new instance.
     *
     * @param builder builder object
     */
    public ListObservationProvider(Builder builder) {
        observations = Collections.unmodifiableList(DomainUtils.softCopyList(builder.observations));
        guardInvariants();
    }

    /**
     * Guards this object to be consistent. Throws exception if this is not the case.
     */
    private void guardInvariants() {
    }

    @Override
    public ObservationIterator getIterator() {
        return new Iterator(observations);
    }

    /**
     * Observation iterator.
     *
     * @param  type of observation
     */
    private static class Iterator implements ObservationIterator {

        /**
         * Iterated observations.
         */
        private List observations;

        /**
         * Current index.
         */
        private AtomicInteger index = new AtomicInteger(0);

        /**
         * Creates new instance.
         *
         * @param observations observations
         */
        public Iterator(List observations) {
            this.observations = observations;
        }

        @Override
        public boolean isNextAvailable() {
            return index.get() < observations.size();
        }

        @Override
        public synchronized T getNext() {
            if (index.get() >= observations.size()) {
                throw new NoSuchElementException("next observation is not available");
            }
            return observations.get(index.getAndIncrement());
        }

        @Override
        public long getNumIterated() {
            return index.get();
        }

        @Override
        public String toString() {
            return ToStringBuilder.reflectionToString(this);
        }

    }

    @Override
    public String toString() {
        return ToStringBuilder.reflectionToString(this);
    }

    /**
     * Creates provider from the list.
     *
     * @param  type of the observation
     * @param observations observations
     * @return created provider
     */
    public static  ListObservationProvider create(List observations) {
        return new ListObservationProvider.Builder().
                setObservations(observations).
                build();
    }

    /**
     * Creates cached observation provider from the specified source observation provider.
     * All observations will be hold in the memory.
     *
     * @param  type of the observation
     * @param source source observation provider
     * @return created provider
     */
    public static  ListObservationProvider createCached(ObservationProvider source) {
        List list = new ArrayList();
        ObservationIterator iterator = source.getIterator();
        while (iterator.isNextAvailable()) {
            list.add(iterator.getNext());
        }
        return new ListObservationProvider.Builder().
                setObservations(list).
                build();
    }

}