从长数组中计算百分位数？

math java statistics percentile apache-commons

2022-09-04 00:43:44

给定一长串以毫秒为单位的延迟，我想从中计算百分位数。我得到了以下方法，这能完成工作，但我不确定如何验证这是否能给我准确的结果？

  public static long[] percentiles(long[] latencies, double... percentiles) {
    Arrays.sort(latencies, 0, latencies.length);
    long[] values = new long[percentiles.length];
    for (int i = 0; i < percentiles.length; i++) {
      int index = (int) (percentiles[i] * latencies.length);
      values[i] = latencies[index];
    }
    return values;
  }

我想从数组中获得第 50、95、99 和 99.9 百分位。latencies

long[] percs = percentiles(latencies, 0.5, 0.95, 0.99, 0.999);

这是在给定长延迟阵列的情况下获得百分位数的正确方法吗？我正在使用Java 7。

答案 1

这就是您要查找的内容：

public static void main(String[] args) {
    List<Long> latencies = new List<Long>() { 3, 6, 7, 8, 8, 9, 10, 13, 15, 16, 20 };
    Collections.sort(latencies);

    System.out.println(percentile(latencies, 25));
    System.out.println(percentile(latencies, 50));
    System.out.println(percentile(latencies, 75));
    System.out.println(percentile(latencies, 100));
}

public static long percentile(List<Long> latencies, double percentile) {
    int index = (int) Math.ceil(percentile / 100.0 * latencies.size());
    return latencies.get(index-1);
}

答案 2

public static double percentile(double percentile, List<Double> items) {
    Preconditions.checkArgument(percentile >= 0);
    Preconditions.checkArgument(percentile <= 100);
    Preconditions.checkArgument(!items.isEmpty());

    Collections.sort(items);
    return items.get((int) Math.round(percentile / 100.0 * (items.size() - 1)));
}


@Test
public void test1() {
    List<Double> list = Arrays.asList(0.0, 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0);
    assertThat(percentile(0, list)).isEqualTo(0.0);
    assertThat(percentile(20, list)).isEqualTo(2.0);
    assertThat(percentile(80, list)).isEqualTo(8.0);
    assertThat(percentile(100, list)).isEqualTo(10.0);
}

@Test
public void test2() {
    List<Double> list = Arrays.asList(0.0, 1.0, 2.0, 3.0);
    assertThat(percentile(51, list)).isEqualTo(2.0);
    assertThat(percentile(49, list)).isEqualTo(1.0);
}

@Test
public void test3() {
    List<Double> list = Arrays.asList(42.0);     
    assertThat(percentile(0, list)).isEqualTo(42.0);
    assertThat(percentile(100, list)).isEqualTo(42.0);
}