Function sum

packages/db-ivm/src/operators/groupBy.ts:151–164

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

 * Creates a sum aggregate function
 */
export function sum<T>(
  valueExtractor: (value: T) => number = (v) => v as unknown as number,
): AggregateFunction<T, number, number> {
  return {
    preMap: (data: T) => valueExtractor(data),
    reduce: (values: Array<[number, number]>) => {
      let total = 0
      for (const [value, multiplicity] of values) {
        total += value * multiplicity
      }
      return total
    },
  }
}

/**
 * Creates a count aggregate function