# series_decompose_forecast()

Forecast based on series decomposition.

Takes an expression containing a series (dynamic numerical array) as input, and predicts the values of the last trailing points. For more information, see series_decompose.

## Syntax

`series_decompose_forecast(`

*Series* `,`

*Points* `[,`

*Seasonality*`,`

*Trend*`,`

*Seasonality_threshold*`])`

## Arguments

*Series*: Dynamic array cell of numeric values. Typically, the resulting output of make-series or make_list operators.*Points*: Integer specifying the number of points at the end of the series to predict (forecast). These points are excluded from the learning (regression) process.*Seasonality*: An integer controlling the seasonal analysis, containing one of:- -1: Autodetect seasonality using series_periods_detect (default).
- period: Positive integer, specifying the expected period in number of bins. For example, if the series is in 1h bins, a weekly period is 168 bins.
- 0: No seasonality (skip extracting this component).

*Trend*: A string controlling the trend analysis, containing one of:`linefit`

: Extract trend component using linear regression (default).`avg`

: Define trend component as average(x).`none`

: No trend, skip extracting this component.

*Seasonality_threshold*: The threshold for seasonality score when*Seasonality*is set to autodetect. The default score threshold is`0.6`

. For more information, see series_periods_detect.

**Return**

A dynamic array with the forecasted series.

Note

- The dynamic array of the original input series should include a number of
*points*slots to be forecasted. The forecast is typically done by using make-series and specifying the end time in the range that includes the timeframe to forecast. - Either seasonality or trend should be enabled, otherwise the function is redundant, and just returns a series filled with zeroes.

## Example

In the following example, we generate a series of four weeks in an hourly grain, with weekly seasonality and a small upward trend. We then use `make-series`

and add another empty week to the series. `series_decompose_forecast`

is called with a week (24*7 points), and it automatically detects the seasonality and trend, and generates a forecast of the entire five-week period.

```
let ts=range t from 1 to 24*7*4 step 1 // generate 4 weeks of hourly data
| extend Timestamp = datetime(2018-03-01 05:00) + 1h * t
| extend y = 2*rand() + iff((t/24)%7>=5, 5.0, 15.0) - (((t%24)/10)*((t%24)/10)) + t/72.0 // generate a series with weekly seasonality and ongoing trend
| extend y=iff(t==150 or t==200 or t==780, y-8.0, y) // add some dip outliers
| extend y=iff(t==300 or t==400 or t==600, y+8.0, y) // add some spike outliers
| make-series y=max(y) on Timestamp from datetime(2018-03-01 05:00) to datetime(2018-03-01 05:00)+24*7*5h step 1h; // create a time series of 5 weeks (last week is empty)
ts
| extend y_forcasted = series_decompose_forecast(y, 24*7) // forecast a week forward
| render timechart
```

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