JavaScript sort array by 2 values

Question

I've an array and I want to sort it by "id" and "date" from smaller to bigger. How can I do this correctly ?

Example :

var unsorted = [
    {id: 1, date: "2015-01-18T15:00:00+01:00"}, 
    {id: 1, date: "2015-01-18T14:30:00+01:00"}, 
    {id: 2, date: "2015-01-18T10:00:00+01:00"}, 
    {id: 1, date: "2015-01-18T16:00:00+01:00"}, 
    {id: 3, date: "2015-01-18T14:15:00+01:00"}, 
    {id: 2, date: "2015-01-18T14:00:00+01:00"}
]

Should return :

var sorted = [
    {id: 1, date: "2015-01-18T14:30:00+01:00"}, 
    {id: 1, date: "2015-01-18T15:00:00+01:00"}, 
    {id: 1, date: "2015-01-18T16:00:00+01:00"}, 
    {id: 2, date: "2015-01-18T10:00:00+01:00"}, 
    {id: 2, date: "2015-01-18T14:00:00+01:00"},
    {id: 3, date: "2015-01-18T14:15:00+01:00"} 
]

ummmm why don't you sort the data using `ORDER BY` when you fetch it from the db on server? — MightyPork, Jan 18 '15 at 19:27
hmm well `array.sort()` takes comparator function as an argument, so try with that. — MightyPork, Jan 18 '15 at 19:31
i've tried many variations and didn't find correct solution, so this why i'm asking here. — robpal, Jan 18 '15 at 19:32
@IGRACH i can't handle data from server side, because i'm getting this data via pubnub and etc.. — robpal, Jan 18 '15 at 19:57

score 7 · Accepted Answer · answered Jan 18 '15 at 19:34

Here is an example using array.sort:

var arr = [
    {id: 1, date: "2015-01-18T15:00:00+01:00"}, 
    {id: 1, date: "2015-01-18T14:30:00+01:00"}, 
    {id: 2, date: "2015-01-18T10:00:00+01:00"}, 
    {id: 1, date: "2015-01-18T16:00:00+01:00"}, 
    {id: 3, date: "2015-01-18T14:15:00+01:00"}, 
    {id: 2, date: "2015-01-18T14:00:00+01:00"}
];

arr.sort(function(a,b){
    if (a.id == b.id) return a.date.localeCompare(b.date);
    return a.id-b.id;    
});

// test
for (var i in arr) {
    console.log(arr[i]);
}

Result being:

 Object {id: 1, date: "2015-01-18T14:30:00+01:00"}
 Object {id: 1, date: "2015-01-18T15:00:00+01:00"}
 Object {id: 1, date: "2015-01-18T16:00:00+01:00"}
 Object {id: 2, date: "2015-01-18T10:00:00+01:00"}
 Object {id: 2, date: "2015-01-18T14:00:00+01:00"}
 Object {id: 3, date: "2015-01-18T14:15:00+01:00"}

Note that depending on how the date is formatted comparing the string representation does not give the same result as comparing the dates. See superpuccio's comment [here](http://stackoverflow.com/a/493018/4178025) for an example. — Diego, Jan 18 '15 at 19:44

James M · Answer 2 · 2015-01-18T19:34:15.780

You can use .sort():

var unsorted = [
    {id: 1, date: "2015-01-18T15:00:00+01:00"}, 
    {id: 1, date: "2015-01-18T14:30:00+01:00"}, 
    {id: 2, date: "2015-01-18T10:00:00+01:00"}, 
    {id: 1, date: "2015-01-18T16:00:00+01:00"}, 
    {id: 3, date: "2015-01-18T14:15:00+01:00"}, 
    {id: 2, date: "2015-01-18T14:00:00+01:00"}
];

var sorted = unsorted.sort(function(a, b) {
    return a.id == b.id ?
        new Date(a.date) - new Date(b.date) : a.id - b.id;
});

console.log(sorted);

Output:

[ { id: 1, date: '2015-01-18T14:30:00+01:00' },
  { id: 1, date: '2015-01-18T15:00:00+01:00' },
  { id: 1, date: '2015-01-18T16:00:00+01:00' },
  { id: 2, date: '2015-01-18T10:00:00+01:00' },
  { id: 2, date: '2015-01-18T14:00:00+01:00' },
  { id: 3, date: '2015-01-18T14:15:00+01:00' } ]

Close, but not quite. The question was to sort an array by 2 attributes. — Ziga Petek, Jan 18 '15 at 19:30

score 3 · Answer 3 · answered Jan 18 '15 at 19:34

Give this a shot

var sorted = unsorted.sort(function(a, b) {
    return a.id === b.id ?
      Date.parse(a.date) - Date.parse(b.date) :
      a.id - b.id ;
});

Explanation

If the id field is equal, we want to return the comparison of the date field.

If the id field is not equal, we will return the comparison of the id field

score 0 · Answer 4 · answered Jan 18 '15 at 19:33

Array.sort takes a function with two parameters to compare two elements of an array. If this function returns a negative then a is placed before b, if it returns positive then a is placed before b and if it returns 0 they stay as they are. Here I compare them by id and if their IDs are same then I compare them by date.

var unsorted = [{
  id: 1,
  date: "2015-01-18T15:00:00+01:00"
}, {
  id: 1,
  date: "2015-01-18T14:30:00+01:00"
}, {
  id: 2,
  date: "2015-01-18T10:00:00+01:00"
}, {
  id: 1,
  date: "2015-01-18T16:00:00+01:00"
}, {
  id: 3,
  date: "2015-01-18T14:15:00+01:00"
}, {
  id: 2,
  date: "2015-01-18T14:00:00+01:00"
}];

unsorted.sort(function(a, b) {
  if (a.id < b.id)
    return -1;
  else if (a.id > b.id)
    return 1;
  else {
    if (a.date < b.date)
      return -1;
    else if (a.date > b.date)
      return 1;
    else
      return 0;
  }
});

score 0 · Answer 5 · answered Jan 18 '15 at 19:40

Divide and conquer!

Start by reducing the input array into a map of id => object, ie:

var dataById = unsorted.reduce(function (soFar, value) {
 // Initialise the array if we haven't processed this
    // id yet.
    if (soFar[value.id] === undefined) {
        soFar[value.id] = [];
    }
  
    // ad this object to Array.
    soFar[value.id].push(value);
  
    return soFar;
}, {});

Now you can sort each array by looping over the Object's keys, note this modifies the dataById map in place.

Object.keys(dataById).forEach(function (id) {
 dataById[id] = dataById[id].sort();
});

Finally, you can combine all the data together, again by iterating over the keys in the map. Note that maps (objects) in javascript don't guarantee the order of their keys, so you may wish to dump the ids out to an Array first before iterating:

var ids = Object.keys(dataById).sort();

// Reduce the ids into an Array of data.
var ids.reduce(function (soFar, value) {
 return soFar.concat(dataById[id]);
}, []);

Not the most efficient way of solving your problem, but hopefully it gives you some help with the thought process.

JavaScript sort array by 2 values

5 Answers5