JSFiddle - React, Tailwind, and code Playground

JavaScript

var mark = [
    [1, 100],
    [2, 400],
    [1, 150],
    [1, 80],
    [2, 100],
    [1, 300],
    [2, 250]
]

    function getResult(arr) {
        var tmp = {};
        for (var i = 0, l = arr.length; i < l; i++) {
            var key = arr[i][0];
            var value = arr[i][1];
            if (!tmp[key]) {
                tmp[key] = 0;
            }
            if (value > tmp[key]) tmp[key] = value;
        }
        return Object.keys(tmp).map(function (el) {
          return [ +el, tmp[el] ];
        });
    }

console.log(getResult(mark));