StatsHelper.java

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// Copyright 2014 Cloudera Inc.
//
// 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.cloudera.impala.util;

public class StatsHelper<T extends Number> {

  private long count_ = 0;

  // Current mean
  private double mean_ = 0.0d;

  // Sum of the square differences from the mean
  private double m2_ = 0.0d;

  public void addSample(T val) {
    ++count_;
    mean_ += (val.doubleValue() - mean_) / count_;
    m2_ += Math.pow(val.doubleValue() - mean_, 2);
  }

  public long count() { return count_; }

  public double mean() {
    return count_ > 0 ? mean_ : 0.0;
  }

  public double variance() {
    return count_ > 1 ? m2_ / (count_ - 1) : 0.0d;
  }

  public double stddev() {
    return Math.sqrt(variance());
  }
}