如需與 Amazon Timestream for LiveAnalytics 類似的功能，請考慮使用 Amazon Timestream for InfluxDB。它提供簡化的資料擷取和單一位數毫秒查詢回應時間，以進行即時分析。[在這裡](https://docs.aws.amazon.com//timestream/latest/developerguide/timestream-for-influxdb.html)進一步了解。

本文為英文版的機器翻譯版本，如內容有任何歧義或不一致之處，概以英文版為準。

# 篩選和減少函數
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Amazon Timestream 支援執行篩選和減少時間序列資料操作的函數。本節提供 Timestream for LiveAnalytics 篩選和減少函數的使用資訊，以及範例查詢。



## 用量資訊
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| 函式 | 輸出資料類型 | Description | 
| --- | --- | --- | 
|  `filter(timeseries(T), function(T, Boolean))`  |  timeseries(T)  |  使用傳遞的 `function`傳回 的值，從輸入時間序列建構時間序列`true`。  | 
|  `reduce(timeseries(T), initialState S, inputFunction(S, T, S), outputFunction(S, R))`  |  R  |  傳回單一值，從時間序列減少。`inputFunction` 將依序在時間序列中的每個元素上調用 。除了採用目前元素之外，inputFunction 也會採用目前狀態 （一開始為 `initialState`)，並傳回新狀態。`outputFunction` 將調用 ，將最終狀態轉換為結果值。`outputFunction` 可以是身分函數。  | 

## 查詢範例
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**Example**  
建立測量值大於 70 的主機和篩選條件點的 CPU 使用率時間序列：  

```
WITH time_series_view AS (
    SELECT INTERPOLATE_LINEAR(
        CREATE_TIME_SERIES(time, ROUND(measure_value::double,2)), 
            SEQUENCE(ago(15m), ago(1m), 10s)) AS cpu_user
    FROM sample.DevOps
    WHERE hostname = 'host-Hovjv' and measure_name = 'cpu_utilization'
        AND time > ago(30m)
    GROUP BY hostname
)
SELECT FILTER(cpu_user, x -> x.value > 70.0) AS cpu_above_threshold
from time_series_view
```

**Example**  
建構主機的 CPU 使用率時間序列，並判斷測量的總和平方：  

```
WITH time_series_view AS (
    SELECT INTERPOLATE_LINEAR(
        CREATE_TIME_SERIES(time, ROUND(measure_value::double,2)), 
            SEQUENCE(ago(15m), ago(1m), 10s)) AS cpu_user
    FROM sample.DevOps
    WHERE hostname = 'host-Hovjv' and measure_name = 'cpu_utilization'
        AND time > ago(30m)
    GROUP BY hostname
)
SELECT REDUCE(cpu_user,
    DOUBLE '0.0',
    (s, x) -> x.value * x.value + s,
    s -> s)
from time_series_view
```

**Example**  
建構主機的 CPU 使用率時間序列，並判斷高於 CPU 閾值的樣本部分：  

```
WITH time_series_view AS (
    SELECT INTERPOLATE_LINEAR(
        CREATE_TIME_SERIES(time, ROUND(measure_value::double,2)), 
            SEQUENCE(ago(15m), ago(1m), 10s)) AS cpu_user
    FROM sample.DevOps
    WHERE hostname = 'host-Hovjv' and measure_name = 'cpu_utilization'
        AND time > ago(30m)
    GROUP BY hostname
)
SELECT ROUND(
    REDUCE(cpu_user, 
      -- initial state 
      CAST(ROW(0, 0) AS ROW(count_high BIGINT, count_total BIGINT)),
      -- function to count the total points and points above a certain threshold
      (s, x) -> CAST(ROW(s.count_high + IF(x.value > 70.0, 1, 0), s.count_total + 1) AS ROW(count_high BIGINT, count_total BIGINT)),
      -- output function converting the counts to fraction above threshold
      s -> IF(s.count_total = 0, NULL, CAST(s.count_high AS DOUBLE) / s.count_total)), 
    4) AS fraction_cpu_above_threshold
from time_series_view
```