locutus/esm/kotlin/collections/runningReduce.js

Locutus other languages' standard libraries to JavaScript for fun and educational purposes

export function runningReduce(values, operation) {
    //  discuss at: https://locutus.io/kotlin/collections/runningReduce/
    // original by: Kevin van Zonneveld (https://kvz.io)
    //      note 1: Returns successive accumulation values from the first element, like Kotlin runningReduce.
    //   example 1: runningReduce([1, 2, 3, 4], (acc, value) => acc + value)
    //   returns 1: [1, 3, 6, 10]
    //   example 2: runningReduce(['a', 'b', 'c'], (acc, value) => acc + value)
    //   returns 2: ['a', 'ab', 'abc']
    //   example 3: runningReduce([], (acc, value) => acc + value)
    //   returns 3: []
    if (typeof operation !== 'function') {
        throw new TypeError('runningReduce(): operation must be a function');
    }
    if (!Array.isArray(values) || values.length === 0) {
        return [];
    }
    const array = values;
    const out = [array[0]];
    let accumulator = array[0];
    for (let i = 1; i < array.length; i++) {
        accumulator = operation(accumulator, array[i], i, array);
        out.push(accumulator);
    }
    return out;
}