核密度估計(jì)函數(shù)采用平滑的峰值函數(shù)來擬合觀察到的數(shù)據(jù)點(diǎn)，從而對真實(shí)的概率分布曲線進(jìn)行模擬。

• 函數(shù)格式

  select kernel_density_estimation(bigint stamp, double value, varchar kernelType)

• 參數(shù)說明

  參數(shù)	說明
  stamp	UnixTime 時(shí)間戳數(shù)據(jù)，單位為秒。
  value	對應(yīng)的觀測數(shù)值。
  kernelType	box：矩形。 epanechnikov：Epanechnikov 曲線。 gaussian：高斯曲線。

• 輸出結(jié)果

  顯示項(xiàng)	說明
  unixtime	對應(yīng)原始數(shù)據(jù)的時(shí)間戳數(shù)據(jù)。
  real	對應(yīng)的觀測數(shù)值。
  pdf	對應(yīng)的每個(gè)觀測點(diǎn)的概率值。

• 示例

  • 代碼示例：

    * | 
    select 
        date_trunc('second', cast(t1[1] as bigint)) as time, t1[2] as real, t1[3] as pdf from (
            select kernel_density_estimation(time, num, 'gaussian') as res from ( 
                select '("__time__" - ("__time__" % 10))' as time, COUNT(*) * 1.0 as num from log group by time order by time)
            ), unnest(res) as t(t1)  limit 1000

  • 結(jié)果示例：