JS create array from a sorted array of pairs

Question

I have this array of pairs in JS :

var my_array = [['line_1','2'],['line_2','3'],['line_3','5'],['line_4','1'],['line_5','4'],]

I would like to sort this array by values and then create a new array with only the sorted keys.

Expected result :

['line_4','line_1','line_2','line_5','line_3']

I tried to sort by using this :

var my_sorted_array = Object.values(my_array).sort((a, b) => a[1] - b[1])

But I don't know how to do the final step and I assume there is a better way to do this in pure JS.

Thanks

Answer 1

You have several methods. If you have a '0' and no gaps, you can use the second method here, which seems to be faster than sort plus map

const start1 = performance.now();
const res1 = my_array
  .sort((a, b) => a[1] - b[1])
  .map(pair => pair[0]);
const end1 = performance.now();  
console.log("1",`Execution time: ${end1 - start1} milliseconds`);

const start2 = performance.now();
const res2 = [];
my_array
  .forEach(pair => res2[pair[1]] = pair[0]);
const end2 = performance.now();  
console.log("2",`Execution time: ${end2 - start2} milliseconds`);

const start3 = performance.now();   
const res3 = my_array
  .reduce((acc, pair) => (acc[pair[1]] = pair[0], acc), []);
const end3 = performance.now();  
console.log("3",`Execution time: ${end3 - start3} milliseconds`);

const start4 = performance.now();   
const res4 = Object.values(Object.fromEntries(my_array.map(([v, k]) => [k, v])));
const end4 = performance.now();  
console.log("4",`Execution time: ${end4 - start4} milliseconds`);

<script>
const lim = 10000; // Set the limit, adjust as necessary
const generateShuffledArray = (lim) => {
    // Generate an array of numbers from 0 to lim-1
    let numbers = Array.from({length: lim}, (_, index) => index);

    // Shuffle the numbers array using the Fisher-Yates (Durstenfeld) shuffle algorithm
    for (let i = numbers.length - 1; i > 0; i--) {
        const j = Math.floor(Math.random() * (i + 1));
        [numbers[i], numbers[j]] = [numbers[j], numbers[i]];
    }

    // Pair each 'line_n' with a unique shuffled number
    let resultArray = numbers.map((num, index) => [`line_${index + 1}`, num.toString()]);

    return resultArray;
}


const my_array = generateShuffledArray(lim);
</script>

Here is a jsperf, I hope I set it up correctly

https://jsperf.app/pazuhe/2