io.mindmaps.graql.internal.query.aggregate.GroupAggregate Maven / Gradle / Ivy

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/*
 * MindmapsDB - A Distributed Semantic Database
 * Copyright (C) 2016  Mindmaps Research Ltd
 *
 * MindmapsDB is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * MindmapsDB is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with MindmapsDB. If not, see .
 *
 */

package io.mindmaps.graql.internal.query.aggregate;

import io.mindmaps.concept.Concept;
import io.mindmaps.graql.Aggregate;

import java.util.Map;
import java.util.stream.Collector;
import java.util.stream.Stream;

import static java.util.stream.Collectors.*;

/**
 * Aggregate that groups results of a match query by variable name, applying an aggregate to each group.
 * @param  the type of each group
 */
class GroupAggregate extends AbstractAggregate, Map> {

    private final String varName;
    private final Aggregate, T> innerAggregate;

    GroupAggregate(String varName, Aggregate, T> innerAggregate) {
        this.varName = varName;
        this.innerAggregate = innerAggregate;
    }

    @Override
    public Map apply(Stream> stream) {
        Collector, ?, T> applyAggregate =
                collectingAndThen(toList(), list -> innerAggregate.apply(list.stream()));

        return stream.collect(groupingBy(result -> result.get(varName), applyAggregate));
    }

    @Override
    public String toString() {
        if (innerAggregate instanceof ListAggregate) {
            return "group $" + varName;
        } else {
            return "group $" + varName + " " + innerAggregate.toString();
        }
    }
}