Removing duplicates in array of objects

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Remove duplicates from an array of objects in javascript

var arr = [{empID:100,empName:greg},{empID:101,empName:Math},{empID:100,empName:greg}];
var sorted_arr = arr.sort(); // You can define the comparing function here. 
                             // JS by default uses a crappy string compare.
var results = [];
for (var i = 0; i < arr.length - 1; i++) {
    if (sorted_arr[i + 1].empID != sorted_arr[i].empID) {
        results.push(sorted_arr[i]);
    }
}

alert(results);

I have an array of objects, but when i try to remove the duplicate object which matches the ID, it does not get removed. What's the issue with the code.

Actually, this should be correct, this is what chrome returns me: `[{"empID":100,"empName":"greg"},{"empID":101,"empName":"Math"}]` If you're talking about the Elements in the results array http://jsbin.com/uwulun/1/edit — Moritz Roessler, Dec 06 '12 at 12:45
Your array probably isn't sorted by `empID`, but by object hash. — Aesthete, Dec 06 '12 at 12:45

score 13 · Accepted Answer · answered Dec 06 '12 at 12:50

13

Your code has two problems:

the sorting does not really work
you forget to add the last element to the result

I would suggest the following alternative:

var arr = ...;
arr.sort( function( a, b){ return a.empID - b.empID; } );

// delete all duplicates from the array
for( var i=0; i<arr.length-1; i++ ) {
  if ( arr[i].empID == arr[i+1].empID ) {
    delete arr[i];
  }
}

// remove the "undefined entries"
arr = arr.filter( function( el ){ return (typeof el !== "undefined"); } );

answered Dec 06 '12 at 12:50

Sirko

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4

Instead of `delete arr[i]` use `arr.splice(i, 1)`. Delete just replaces that item with "undefined" but doesn't removeit from the array. – Adam Grant Jul 16 '13 at 17:29
@ajkochanowicz Though I do not have any evidence, I think the above code is better as it only creates a new array once, whereas using `splice()` would create a new array every time a duplicate is found. (and thus trigger unnecessary GC runs). – Sirko Jul 16 '13 at 18:53
Actually, it is nice that the indexes of each array item don't change--which can be dangerous in the middle of a loop. – Adam Grant Jul 16 '13 at 19:15
You can also check for arr[i+1] inside the loop to not be undefined like this: if ( arr[i+1] && arr[i].empID === arr[i+1].empID ). This is inportant when the loop goes to the last item. – Yura Loginov Nov 11 '13 at 11:49

score 6 · Answer 2 · answered Dec 06 '12 at 13:05

Provided that empID is guaranteed to be a string or number, I would skip the sorting step and use an object as a hash of IDs that have already been seen:

var arr = [
    {empID:100,empName:"greg"},
    {empID:101,empName:Math},
    {empID:100,empName:"greg"}
];

var results = [];
var idsSeen = {}, idSeenValue = {};
for (var i = 0, len = arr.length, id; i < len; ++i) {
    id = arr[i].empID;
    if (idsSeen[id] !== idSeenValue) {
        results.push(arr[i]);
        idsSeen[id] = idSeenValue;
    }
}

score 1 · Answer 3 · answered Dec 06 '12 at 12:50

Your sort function should really use a comparator, if you're going to be comparing items n and n+1

var sorted_arr = arr.sort(function(a,b) { return a.empID - b.empID; } );

This way you can be assured that sequential items in the list can possibly have duplicate empID properties.

Removing duplicates in array of objects

3 Answers3

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