Function avg

packages/db-ivm/src/operators/groupBy.ts:188–212

(
  valueExtractor: (value: T) => number = (v) => v as unknown as number,
)

 * Creates an average aggregate function
 */
export function avg<T>(
  valueExtractor: (value: T) => number = (v) => v as unknown as number,
): AggregateFunction<T, number, { sum: number; count: number }> {
  return {
    preMap: (data: T) => ({
      sum: valueExtractor(data),
      count: 0,
    }),
    reduce: (values: Array<[{ sum: number; count: number }, number]>) => {
      let totalSum = 0
      let totalCount = 0
      for (const [value, multiplicity] of values) {
        totalSum += value.sum * multiplicity
        totalCount += multiplicity
      }
      return {
        sum: totalSum,
        count: totalCount,
      }
    },
    postMap: (result: { sum: number; count: number }) => {
      return result.sum / result.count
    },
  }
}

type CanMinMax = number | Date | bigint | string