Removing duplicates in array of objects [duplicate]

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Possible Duplicate:
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 jsbin.com/uwulun/1/edit — Moritz Roessler
– Moritz Roessler, Commented Dec 6, 2012 at 12:45
Your array probably isn't sorted by empID, but by object hash. — Aesthete
– Aesthete, Commented Dec 6, 2012 at 12:45

Sirko · Accepted Answer · 2012-12-06 12:50:20Z

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 6, 2012 at 12:50

Sirko

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4 Comments

Adam Grant Over a year ago

Instead of delete arr[i] use arr.splice(i, 1). Delete just replaces that item with "undefined" but doesn't removeit from the array.

Sirko Over a year ago

@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).

Adam Grant Over a year ago

Actually, it is nice that the indexes of each array item don't change--which can be dangerous in the middle of a loop.

Yura Loginov Over a year ago

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.

Tim Down · Accepted Answer · 2012-12-06 13:05:33Z

6

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;
    }
}

answered Dec 6, 2012 at 13:05

Tim Down

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Comments

Aesthete · Accepted Answer · 2012-12-06 12:50:02Z

1

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.

answered Dec 6, 2012 at 12:50

Aesthete

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