Grouping price levels by ticket size

grouping.js

/* const levels = [
    [1001, 1],
    [1000.5, 1],
    [1000, 1],
    [999, 1],
    [988.5, 1],
    [988, 1]
] */

const levels = [
    [50163, 110],
    [50162, 13140],
    [50158,  3763],
    [50156,  1570],
    [50155, 21997],
    [50152.5, 450],
    [50151,  4669],
    [50150.5, 10329],
    [50150,  2500],
    [50149.5, 450],
    [50149,  4022],
    [50148, 20000],
    [50147,  5166],
    [50146.5,5274],
    [50145,174609],
    [50143, 20000],
    [50141, 28000],
    [50140.5,5000],
    [50138,  6000],
    [50132.5,4529],
    [50132,  4755],
    [50131, 12483],
    [50128.5,61115],
    [50128, 23064],
    [50125.5,181363]
]

/**
 * Returns the number rounded to the nearest interval.
 * Example:
 * 
 *   roundToNearest(80, 100); // 100
 *   roundToNearest(25, 15);  // 30
 * 
 * @param {number} value    The number to round
 * @param {number} interval The numeric interval to round to
 * @return {number}
 */
function roundToNearest(value, interval) {
    return Math.floor(value / interval) * interval;
}

function groupByPrice(levels) {
    return levels.map((level, idx) => {
        const nextLevel = levels[idx + 1];
        const prevLevel = levels[idx - 1];

        if(nextLevel && level[0] === nextLevel[0]) {
            return [level[0], level[1] + nextLevel[1]]
        } else if(prevLevel && level[0] === prevLevel[0]) {
            return [];
        } else {
            return level;
        }
    }).filter(el => el.length > 0);
}

function groupByTicketSize(levels, ticketSize) {
    return groupByPrice(levels.map(level => [roundToNearest(level[0], ticketSize), level[1]]));
}


// console.log(groupByTicketSize(levels, 0.5));
// console.log(groupByTicketSize(levels, 1));
// console.log(groupByTicketSize(levels, 2.5));
console.log(groupByPrice([ [1000, 100], [1000, 200], [993, 20] ]));