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Core package for Neo4j Procedures

There is a newer version: 5.24.0

/*
 * Copyright (c) "Neo4j"
 * Neo4j Sweden AB [http://neo4j.com]
 *
 * This file is part of Neo4j.
 *
 * 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 apoc.agg;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import org.neo4j.procedure.*;

/**
 * @author mh
 * @since 18.12.17
 */
public class Median {
    @UserAggregationFunction("apoc.agg.median")
    @Description("Returns the mathematical median for all non-null `INTEGER` and `FLOAT` values.")
    public MedianFunction median() {
        return new MedianFunction();
    }

    public static class MedianFunction {
        private List values = new ArrayList<>();

        @UserAggregationUpdate
        public void aggregate(@Name("value") Object value) {
            if (value instanceof Number) {
                values.add(((Number) value).doubleValue());
            }
        }

        @UserAggregationResult
        public Object result() {
            if (values.isEmpty()) return null;
            Collections.sort(values);
            int size = values.size();
            if (size % 2 == 1) {
                return values.get(size / 2);
            } else {
                return (values.get(size / 2 - 1) + values.get(size / 2)) / 2D;
            }
        }
    }
}