Function reduce

reduce<T>(object, fn): T
Summarize all values in an iterable using a reducer function.
Type Parameters
- T
Parameters
- object: Iterable<T>
  The iterable object of interest.
- fn: ((accumulator, value, index) => T)
  The reducer function to invoke for each value.
  - - (accumulator, value, index): T
    - Parameters
      accumulator: T
      value: T
      index: number
      Returns T
Returns T
The final accumulated value.

Notes
The reduce function follows the conventions of Array#reduce.

If the iterator is empty, an initial value is required. That value will be used as the return value. If no initial value is provided, an error will be thrown.

If the iterator contains a single item and no initial value is provided, the single item is used as the return value.

Otherwise, the reducer is invoked for each element in the iterable. If an initial value is not provided, the first element will be used as the initial accumulated value.

Complexity
Linear.

Example
```
import { reduce } from '@lumino/algorithm';

let data = [1, 2, 3, 4, 5];

let sum = reduce(data, (a, value) => a + value);  // 15
```
- Defined in reduce.ts:48
reduce<T, U>(object, fn, initial): U
Type Parameters
- T
- U
Parameters
- object: Iterable<T>
- fn: ((accumulator, value, index) => U)
  - - (accumulator, value, index): U
    - Parameters
      accumulator: U
      value: T
      index: number
      Returns U
- initial: U
Returns U
- Defined in reduce.ts:52