Array sorting in Javascript with nested objects

Question

I have an array of objects which I need to sort in 2 ways as stated below:

Sort by alphabetical order using the country name.
Inside every country sort scores in ascending order.

Below is the array and what I have tried to do.

//Structure of the Array
let allCountryScores=[
   {
      name: "Ethiopia", 
      scores:  [ {n: "Sub", s: 9990}, {n: "lucy", s: "4134234"}, {n: "DWH", s: 9999},  {n: "Hanif", s: 999999999} ]
    },     

]

//MY Code below

//Alphabetic ordering countries

let orderedCountries = allCountryScores.sort((a, b) => a.name.localeCompare(b.name));
//Numeric ordering of scores
let orderedScores = orderedCountries.forEach(country => { country.scores.sort((a, b) => a.s > b.s) });
console.log(orderedScores);

In my console, I am getting undefined. What could be wrong with my code?

forEach() doesn't return anything. You also have no return statement in the country => { ... } function. — Barmar
– Barmar, Commented Aug 25, 2021 at 16:35
Also keep in mind that while the first sort does assign the sorted array to orderedCountries it is not a new array, but the mutated original array. — pilchard
– pilchard, Commented Aug 25, 2021 at 16:38
@Barmar I have added the return keyword but my array is only sorting using the first criteria only — Kudah Shambare
– Kudah Shambare, Commented Aug 25, 2021 at 16:40
You also need to change forEach to map, since forEach doesn't return what the callback function returns. — Barmar
– Barmar, Commented Aug 25, 2021 at 16:44

T.J. Crowder · Accepted Answer · 2021-08-25 16:38:20Z

There are two issues:

forEach always returns undefined. You don't need the assignment on that line, just remove it. (You also don't need the assignment on the previous line, sort works on the array in place.)
You're not sorting the scores correctly, a.s > b.s doesn't return what sort expects from its callback (a negative number if a should come before b, a positive number if a should come after b, or 0 if their order doesn't matter). a.s - b.s does return that number.

Here's an updated version assuming you're happy to modify your original arrays:

//Alphabetic ordering countries
allCountryScores.sort((a, b) => a.name.localeCompare(b.name));
//Numeric ordering of scores
allCountryScores.forEach(country => { country.scores.sort((a, b) => a.s - b.s) });
console.log(allCountryScores);

Live Copy:

//Structure of the Array
let allCountryScores=[
   {
      name: "Ethiopia", 
      scores:  [ {n: "Sub", s: 9990}, {n: "lucy", s: "4134234"}, {n: "DWH", s: 9999},  {n: "Hanif", s: 999999999} ]
    },     

]

//Alphabetic ordering countries
allCountryScores.sort((a, b) => a.name.localeCompare(b.name));
//Numeric ordering of scores
allCountryScores.forEach(country => { country.scores.sort((a, b) => a.s - b.s) });
console.log(allCountryScores);

.as-console-wrapper {
    max-height: 100% !important;
}

If you want to create new arrays containing new objects with new arrays in them instead, you can do it like this:

const countries =
    allCountryScores.map(({name, scores}) => {
        // Copy and sort the scores
        scores = [...scores].sort((a, b) => a.s - b.s);
        // Return a new object
        return {name, scores};
    })
    // Sort that new array of countries
    .sort((a, b) => a.name.localeCompare(b.name));

Live Copy:

//Structure of the Array
let allCountryScores=[
   {
      name: "Ethiopia", 
      scores:  [ {n: "Sub", s: 9990}, {n: "lucy", s: "4134234"}, {n: "DWH", s: 9999},  {n: "Hanif", s: 999999999} ]
    },     

]

const countries =
    allCountryScores.map(({name, scores}) => {
        // Copy and sort the scores
        scores = [...scores].sort((a, b) => a.s - b.s);
        // Return a new object
        return {name, scores};
    })
    // Sort that new array of countries
    .sort((a, b) => a.name.localeCompare(b.name));

console.log(countries);

.as-console-wrapper {
    max-height: 100% !important;
}

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