Filter out multi-dimensional arrays

filter array

console.time("filter");
let cat = ([].concat.apply([], this.transits.map(item => item.categories))).filter((value, index, self) => self.indexOf(value) === index);
console.timeEnd("filter");

console.time("set");
let cat2 = [...new Set([].concat.apply([], this.transits.map(item => item.categories)))];
console.timeEnd("set");

console.time("flat")
let cat3 = [...new Set(this.transits.map(item => item.categories).flat())];
console.timeEnd("flat")

console.log(cat, cat2, cat3)