public static Map interpolate()

in ambari-metrics-common/src/main/java/org/apache/hadoop/metrics2/sink/timeline/PostProcessingUtil.java [85:158]
46 lines of code
16 McCabe index (conditional complexity)

  public static Map<Long, Double> interpolate(Map<Long, Double> valuesMap, List<Long> requiredTimestamps) {

    LinearInterpolator linearInterpolator = new LinearInterpolator();

    if (valuesMap == null || valuesMap.isEmpty()) {
      return null;
    }
    if (requiredTimestamps == null || requiredTimestamps.isEmpty()) {
      return null;
    }

    Map<Long, Double> interpolatedValuesMap = new HashMap<>();

    if (valuesMap.size() == 1) {
      //Just one value present in the window. Use that value to interpolate all required timestamps.
      Double value  = null;
      for (Map.Entry<Long, Double> entry : valuesMap.entrySet()) {
        value = entry.getValue();
      }
      for (Long requiredTs : requiredTimestamps) {
        interpolatedValuesMap.put(requiredTs, value);
      }
      return interpolatedValuesMap;
    }

    double[] timestamps = new double[valuesMap.size()];
    double[] metrics = new double[valuesMap.size()];

    int i = 0;
    for (Map.Entry<Long, Double> entry : valuesMap.entrySet()) {
      timestamps[i] = (double) entry.getKey();
      metrics[i++] = entry.getValue();
    }

    PolynomialSplineFunction function = linearInterpolator.interpolate(timestamps, metrics);
    PolynomialFunction[] splines = function.getPolynomials();
    PolynomialFunction first = splines[0];

    for (Long requiredTs : requiredTimestamps) {

      Double interpolatedValue = null;
      if (timestampInRange(requiredTs, timestamps[0], timestamps[timestamps.length - 1])) {
        /*
          Interpolation Case
          Required TS is within range of the set of values used for interpolation.
          Hence, we can use library to get the interpolated value.
         */
        interpolatedValue = function.value((double) requiredTs);
      } else {
        /*
        Extrapolation Case
        Required TS outside range of the set of values used for interpolation.
        We will use the coefficients to make best effort extrapolation
        y(x)= y1 + m * (x−x1)
        where, m = (y2−y1)/(x2−x1)
         */
        if (first.getCoefficients() != null && first.getCoefficients().length > 0) {
          /*
          y = c0 + c1x
          where c0, c1 are coefficients
          c1 will not be present if slope is zero.
           */
          Double y1 = first.getCoefficients()[0];
          Double m = (first.getCoefficients().length > 1) ? first.getCoefficients()[1] : 0.0;
          interpolatedValue = y1 + m * (requiredTs - timestamps[0]);
        }
      }

      if (interpolatedValue != null && interpolatedValue >= 0.0) {
        interpolatedValuesMap.put(requiredTs, interpolatedValue);
      }
    }
    return interpolatedValuesMap;
  }