89 lines
3.0 KiB
Markdown
89 lines
3.0 KiB
Markdown
---
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title: doubleEMA() function
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description: >
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The `doubleEMA()` function calculates the exponential moving average of values
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grouped into `n` number of points, giving more weight to recent data at double
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the rate of `exponentialMovingAverage()`.
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aliases:
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- /influxdb/v2.0/reference/flux/functions/built-in/transformations/aggregates/doubleema/
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- /influxdb/v2.0/reference/flux/stdlib/built-in/transformations/aggregates/doubleema/
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- /influxdb/v2.0/reference/flux/stdlib/built-in/transformations/doubleema/
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- /influxdb/cloud/reference/flux/stdlib/built-in/transformations/doubleema/
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menu:
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flux_0_x_ref:
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name: doubleEMA
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parent: universe
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weight: 102
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flux/v0.x/tags: [transformations]
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related:
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- /flux/v0.x/stdlib/universe/movingaverage/
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- /flux/v0.x/stdlib/universe/tripleema/
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- /flux/v0.x/stdlib/universe/timedmovingaverage/
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- /flux/v0.x/stdlib/universe/exponentialmovingaverage/
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- /{{< latest "influxdb" "v1" >}}/query_language/functions/#double-exponential-moving-average, InfluxQL DOUBLE_EXPONENTIAL_MOVING_AVERAGE()
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introduced: 0.38.0
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---
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The `doubleEMA()` function calculates the exponential moving average of values in
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the `_value` column grouped into `n` number of points, giving more weight to recent
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data at double the rate of [`exponentialMovingAverage()`](/flux/v0.x/stdlib/universe/exponentialmovingaverage/).
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```js
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doubleEMA(n: 5)
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```
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##### Double exponential moving average rules
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- A double exponential moving average is defined as `doubleEMA = 2 * EMA_N - EMA of EMA_N`.
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- `EMA` is an exponential moving average.
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- `N = n` is the period used to calculate the EMA.
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- A true double exponential moving average requires at least `2 * n - 1` values.
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If not enough values exist to calculate the double EMA, it returns a `NaN` value.
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- `doubleEMA()` inherits all [exponential moving average rules](/flux/v0.x/stdlib/universe/exponentialmovingaverage/#exponential-moving-average-rules).
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## Parameters
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### n {data-type="int"}
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Number of points to average.
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### tables {data-type="stream of tables"}
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Input data.
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Default is piped-forward data ([`<-`](/flux/v0.x/spec/expressions/#pipe-expressions)).
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## Examples
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{{% flux/sample-example-intro %}}
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#### Calculate a three point double exponential moving average
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```js
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import "sampledata"
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sampledata.int()
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|> doubleEMA(n: 3)
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```
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{{< expand-wrapper >}}
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{{% expand "View input and output" %}}
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{{< flex >}}
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{{% flex-content %}}
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##### Input data
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{{% flux/sample set="int" %}}
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{{% /flex-content %}}
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{{% flex-content %}}
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##### Output data
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| _time | tag | _value |
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| :------------------- | :-- | -----------------: |
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| 2021-01-01T00:00:40Z | t1 | 16.627222222222223 |
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| 2021-01-01T00:00:50Z | t1 | 8.301527777777778 |
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| _time | tag | _value |
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| :------------------- | :-- | -----------------: |
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| 2021-01-01T00:00:40Z | t2 | 15.907222222222224 |
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| 2021-01-01T00:00:50Z | t2 | 5.941527777777779 |
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{{% /flex-content %}}
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{{< /flex >}}
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{{% /expand %}}
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{{< /expand-wrapper >}}
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