GroupCountPipe.java

package com.tinkerpop.pipes.sideeffect;

import com.tinkerpop.pipes.AbstractPipe;

import java.util.HashMap;
import java.util.Map;

/**
 * The GroupCountPipe will simply emit the incoming object, but generate a map side effect.
 * The map's keys are the objects that come into the pipe.
 * The map's values are the number of times that the key object has come into the pipe.
 *
 * @author Marko A. Rodriguez (http://markorodriguez.com)
 */
public class GroupCountPipe<S> extends AbstractPipe<S, S> implements SideEffectPipe.GreedySideEffectPipe<S, Map<S, Number>> {

    private Map<S, Number> countMap;

    public GroupCountPipe(final Map<S, Number> countMap) {
        this.countMap = countMap;
    }

    public GroupCountPipe() {
        this.countMap = new HashMap<S, Number>();
    }

    protected S processNextStart() {
        final S s = this.starts.next();
        this.updateMap(s);
        return s;
    }

    public Map<S, Number> getSideEffect() {
        return this.countMap;
    }

    private void updateMap(final S s) {
        final Number temp = this.countMap.get(s);
        if (null == temp) {
            this.countMap.put(s, 1l);
        } else {
            this.countMap.put(s, 1l + temp.longValue());
        }
    }

    public void reset() {
        this.countMap = new HashMap<S, Number>();
        super.reset();
    }
}