JSFiddle - React, Tailwind, and code Playground

JavaScript

var array = [
 {season:  1, episode:  2, notes: "..."},
 {season:  1, episode:  2, notes: "..."},
 {season:  1, episode:  1, notes: "..."},
 {season: -1, episode: -1, notes: "..."},
 {season: -1, episode: -1, notes: "..."},
 {season: -1, episode: -1, notes: "..."},
 {season:  3, episode:  1, notes: "..."},
 {season:  13, episode:  12, notes: "..."},
 {season:  2, episode:  1, notes: "..."}
];
    
var grouped = _.groupBy(array, function (el) { 
    var s = el.season,
        e = el.episode;
    return "S" + (s > 0 && s < 10 ? "0" : "") + s +
           " E" + (e > 0 && e < 10 ? "0" : "") + e;
});
_.sortBy(Object.keys(grouped), function (el) { return el; }).forEach(function (key) {
    console.log(key + ": ");
    console.log(grouped[key]);
});