Sort an array with JS objects in it by two values

Question

I have an array with roughly 50 JS objects inside, each object in the array has a name, catname, dish_sort_id and sort_id

currently i am trying to sort it so that in the array it goes group objects via catname and if dish_sort_id < then dish_sort_id of next object. Below is the code i am using to sort the array

despite using this code some items are appearing in the wrong order, but they are being sorted

A.sort(function(a,b){
        if(a.catname == b.catname && a.dish_sort_id > b.dish_sort_id){
            return -1;
        } else if(a.catname == b.catname && a.dish_sort_id < b.dish_sort_id){
            return 1;
        } else if(a.catname == b.catname && a.dish_sort_id == b.dish_sort_id){
            return 0;
        }
    });

Okay. And you're here because... ? Btw, if a and b guaranteed to have equal catname for all entries - why do you still compare them? And if they are not - where is the corresponding return for such a case? — zerkms
– zerkms, Commented Apr 24, 2015 at 10:59
Edit the question and add the expected and actual output. That will make some things clear. — LittlePanda
– LittlePanda, Commented Apr 24, 2015 at 11:02
No they are different basically what is happening is to sort them by the catname and in order of dish_sort_id e.g. food 1 food 2 food 3 then drink 1 drink 2 and so on — Ryan K
– Ryan K, Commented Apr 24, 2015 at 11:02
If they are different - why don't you compare them? Do you realize you return undefined in case if they are different? Are you aware that Array.prototype.sort() callback MUST return one of {-1, 0, 1}? — zerkms
– zerkms, Commented Apr 24, 2015 at 11:03
Well, what do you think happens if the a.catname == b.catname comparison is not true? — zerkms
– zerkms, Commented Apr 24, 2015 at 11:05

T.J. Crowder · Accepted Answer · 2015-04-24 11:11:11Z

Your callback is breaking the contract: It doesn't return anything if catname is the same on the two objects you're comparing. And separate from breaking the contract, that's also why it's not working correctly.

This is a standard case of a multi-key sort, which you do by the first key, then the second key, etc. For instance, this sorts by catname (ascending) and, within catnames, by dish_sort_id (descending, as that seemed to be what your code did):

A.sort(function(a,b){
    var rv = a.catname.localeCompare(b.catname);
    if (rv == 0) {
        // Same name, use the dish_sort_id
        rv = b.dish_sort_id - a.dish_sort_id;
    }
    return rv;
});

Live example:

var name1 = randomName();
var name2 = randomName();
var A = [
    { catname: name2, dish_sort_id: randomNumber() },
    { catname: name1, dish_sort_id: randomNumber() },
    { catname: name1, dish_sort_id: randomNumber() },
    { catname: name2, dish_sort_id: randomNumber() },
    { catname: name2, dish_sort_id: randomNumber() },
    { catname: name1, dish_sort_id: randomNumber() }
];
show("Before", A);
A.sort(function(a,b){
    var rv = a.catname.localeCompare(b.catname);
    if (rv == 0) {
        // Same name, use the dish_sort_id
        rv = b.dish_sort_id - a.dish_sort_id;
    }
    return rv;
});
snippet.log("----");
show("After", A);

function show(label, a) {
  snippet.log(label + ":");
  A.forEach(function(entry) {
      snippet.log(entry.catname + " - " + entry.dish_sort_id);
  });
}

function randomName() {
    var rv = "";
    while (rv.length < 5) {
        rv += String.fromCharCode(65 + Math.floor(Math.random() * 26));
    }
    return rv;
}
function randomNumber() {
    return Math.floor(Math.random() * 10);
}

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<script src="http://tjcrowder.github.io/simple-snippets-console/snippet.js"></script>

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