ZscoreActor

The ZscoreActor (Z-score actor) is a Coral Actor that determines whether or not a value from an event is an outlier. The statistics actor state is used for the average and standard deviation of the measurement value.

Creating the actor

The ZscoreActor has type: "zscore". The params value is a JSON with a single field:

field	type	required	description
`by`	string	yes	the name of the grouping field
`field`	string	yes	the name of measurement field
`score`	float	yes	the value of the threshold for outliers

Example

{
  "type": "zscore",
  "params": {
    "by": "tag",
    "field": "amount",
    "score" : 6.0
  }
}

This will create a Z-score component monitoring the amount field. If the amount is more than 6 standard deviations away from the mean, the object is emitted.

Note that this actor implicitly assumes that the data is normally distributed. You can still use this actor if your data is not normally distributed, but we are not sure how the result should be interpreted in that case.

Trigger

The ZscoreActor accepts as trigger a JSON with a value for the specified field.

Emit

The ZscoreActor emits the input but only when the value is considered an outlier.

State

The ZscoreActor keeps no state.

Collect

The ZscoreActor collects state from the StatsActor for the field it monitors. The count, average and standard deviation values are used to determine whether or not the trigger value is an outlier.

Timer

The ZscoreActor does not provide timer actions.