MeanReducer.java

// Copyright 2016 Twitter. All rights reserved.
//
// 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 com.twitter.heron.api.metric;

public class MeanReducer implements IReducer<MeanReducerState, Number, Double> {
  public MeanReducerState init() {
    return new MeanReducerState();
  }

  public MeanReducerState reduce(MeanReducerState acc, Number input) {
    acc.count++;
    acc.sum += input.doubleValue();
    return acc;
  }

  public Double extractResult(MeanReducerState acc) {
    if (acc.count > 0) {
      return acc.sum / (double) acc.count;
    } else {
      return null;
    }
  }
}