Linreg Prediction Unit
The linreg unit takes one optional paramater, pre_filter:
"pre_filter" :
{ "aggregate": "min" | "max" | "avg"
, "interval": Number
, "interval_start": Number
}If this parameter is present then the input data is filtered.
interval and interval_start are in seconds; interval marks the length of the interval the filter aggragate function is applied to. So to filter maximum values for every hour you’d say aggregate = "max" and interval = 3600.
interval_start specifies interval start boundaries. In other words, it is an offset added to every epoch value before determining the interval it belongs to. So if for example interval_start = 0 and interval = 86400 (a day) then the timeframe 00:00 - 23:59 (UTC!) form one interval; the boundaries are every midnight (UTC).
To have filter boundaries eg. every day at 6:00 EEST (UTC+03:00), that is, 3:00 UTC, you would have interval_start = -10800 and interval = 86400. (3 * 3600 = 10800). Note that interval_start is negative, as it is an offset forward in the original data values to match boundaries.
(Sidenote: interval_start := interval_start modulo interval)
The full filter example:
"pre_filter" :
{ "aggregate": "min"
, "interval": 86400
, "interval_start": -10800
}If, either the first or last interval is incomplete that interval is discarded when doing predictions. An incomplete interval here means that there it has a subinterval at least half the length of the original that has no data points in it.