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AggregateReplace

The AggregateReplace type describes a function that can be used to optimize a custom Aggregate by providing a shortcut for when a single value in the input values is replaced with another.

(
  metric: Metric,
  add: number,
  remove: number,
  length: number,
): Metric | undefined
TypeDescription
metricMetric

The current value of the Metric.

addnumber

The number being added to the Metric's aggregation.

removenumber

The number being removed from the Metric's aggregation.

lengthnumber

The length of the array of numbers in the Metric's aggregation.

returnsMetric | undefined

The new value of the Metric.

Some aggregation functions do not need to recalculate the aggregation of the whole set when one value changes. For example, when replacing a number in a series, the new sum of the series is the previous sum, plus the new value, minus the old value.

If it is not possible to shortcut the aggregation based on just one value changing, return undefined and the Metric will be completely recalculated.

Where possible, if you are providing a custom Aggregate, seek an implementation of an AggregateReplace function that can reduce the complexity cost of changing the input data set in place. See the setMetricDefinition method for more examples.