reduceFinalize

This method works like the built-in reduce method, but allows transforming the final value before returning it.

reduceFinalize(reducer, finalizer, initValue?)

• reducer - a callback with signature (accumulatedValue, currentValue, index, array)
• finalizer - a callback with signature (producedValue, array)
• initValue - an optional parameter being an initial value for the reducer function, it may be assigned a value or a callback that returns value (then its signature is (array))

Examples

Calculating a Mean

const arr = [1,2,3,4];
const mean = arr.reduceFinalize(
  (acc,curr) => acc + curr,
  (sum,seq) => sum / seq.length
);

console.log(mean);
// 2.5

• or with use of the object that contains temporary data to latter use:

const arr = [1,2,3,4];
const mean = arr.reduceFinalize(
  (acc,curr) => ({
    sum: acc.sum + curr,
    elements: acc.elements + 1
  }),
  (obj) => obj.sum / obj.elements,
  { sum: 0, elements: 0 }
);

console.log(mean);
// 2.5

• alternatively:

const arr = [1,2,3,4];
const mean = arr.reduceFinalize(
  (acc,curr) => ({
    sum: (acc.sum || 0) + curr,
    elements: (acc.elements || 0) + 1
  }),
  (obj) => obj.sum / obj.elements,
  {}
);

console.log(mean);
// 2.5

Getting Index of Max Value

const nums = [2,4,1,8,3,8];
const indexOfMax = nums.reduceFinalize(
  (acc,curr,idx) => {
    if (curr > acc.value) {
      return {
        value: curr, index: idx
      };
    } else return acc;
  },
  ({index}) => index,
  ([first]) => ({ value: first, index: 0 })
);

console.log(indexOfMax);
// 3