Javascript remove array objects with duplicate properties while keeping the latest occurance

Question

I've searched a lot for this but couldn't find anything that match my requirement.

I want to remove all the duplicates but keeping the last entry not the first.

The array is already presorted I don't want to mess with sorting

So it looks like this :

[{
    name:"Joe",
    status:"foo1" },
  {
    name:"Joe",
    status:"foo2"},
  {
     name:"Vani",
    status:"foo5"
  }]

The expected output looks like:

  [{
    name:"Joe",
    status:"foo2"},
  {
     name:"Vani",
    status:"foo5"
  }]

I'd be thankful if someone can help me!

Perhaps try reversing the array, then try any other method that keeps the first value. You can then reverse it back — jro
– jro, Commented Mar 13, 2019 at 11:16
Welcome to Stack Overflow! Please take the tour (you get a badge!) and read through the help center, in particular How do I ask a good question? Your best bet here is to do your research, search for related topics on SO, and give it a go. If you get stuck and can't get unstuck after doing more research and searching, post a minimal reproducible example of your attempt and say specifically where you're stuck. People will be glad to help. — T.J. Crowder
– T.J. Crowder, Commented Mar 13, 2019 at 11:17
The array is already pre-sorted I don't want to mess with sorting! , I will add this above — HUJ
– HUJ, Commented Mar 13, 2019 at 11:18

prasanth · Accepted Answer · 2019-03-13 11:20:27Z

3

You can simply use reduce

let arr = [{ name:"Joe", status:"foo1" }, { name:"Joe", status:"foo2"}, { name:"Vani", status:"foo5" }]

let op = arr.reduce((op,inp)=>{
  op[inp.name] = inp
  return op
},{})

console.log(Object.values(op))

edited Mar 13, 2019 at 11:20

prasanth

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answered Mar 13, 2019 at 11:18

Code Maniac

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1 Comment

Mohammad Usman Over a year ago

It is not guaranteed that values in array returned by Object.values() will preserve the same order as in input array.

Mohammad Usman · Accepted Answer · 2019-03-13 11:28:40Z

2

You can make use of ES6 Map. As from Docs:

The Map object holds key-value pairs and remembers the original insertion order of the keys. Any value (both objects and primitive values) may be used as either a key or a value.

const data = [
  { name:"Joe", status:"foo1" },
  { name:"Joe", status:"foo2" },
  { name:"Vani", status:"foo5" }
];

const removeDupes = (arr, map = new Map()) => {
  arr.forEach(o => map.set(o.name, o));

  return [...map.values()];
};

console.log(removeDupes(data));

.as-console-wrapper { max-height: 100% !important; top: 0; }

edited Mar 13, 2019 at 11:28

answered Mar 13, 2019 at 11:22

Mohammad Usman

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Comments

Praveenkumar Kalidass · Accepted Answer · 2019-03-13 12:29:02Z

0

Try using simple forEach,

const arr = [{ name:"Joe", status:"foo1" }, { name:"Joe", status:"foo2"}, { 
    name:"Vani", status:"foo5" }];

let result = {};
arr.forEach((val) => { result[val.name] = val; });

console.log(Object.values(result));

Hope this helps...

edited Mar 13, 2019 at 12:29

answered Mar 13, 2019 at 12:00

Praveenkumar Kalidass

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Comments

Ryan Barker · Accepted Answer · 2022-10-26 06:01:04Z

The accepted answer doesn't actually keep the order, it amends the object at the initially found index

You could amend it to look like this:

const data = [
  { name:"Joe", status:"foo1" },
  { name:"Vani", status:"foo2" },
  { name:"Joe", status:"foo3" }
];

const removeDupes = (arr, map = new Map()) => {
  arr.forEach((o, i) => map.set(o.name, {...o, order: i}));

  return [...map.values()].sort((a, b) => a.order - b.order);
};

console.log(removeDupes(data));

Or perhaps do something more simple like:

const data = [
  { name:"Joe", status:"foo1" },
  { name:"Vani", status:"foo2" },
  { name:"Joe", status:"foo3" }
];

let newData = [];
data.forEach(x => {
  newData = newData.filter(y => y.name != x.name);
  newData.push(x);
});

console.log(newData);

I'll let someone else figure out a more performant solution...

You · Accepted Answer · 2024-01-02 10:16:16Z

0

// remove duplicate while preserve order
array.filter((row, i, arr) => arr.slice(0, i).findIndex((l) => l === row) === -1)
// change `l === row` to your own comparison logic

In your case:

const data = [
  {
    name:"Joe",
    status:"foo1"
  },
  {
    name:"Joe",
    status:"foo2"
  },
  {
    name:"Vani",
    status:"foo5"
  }
];

const duplicateRemoved = data
  .toReversed()
  .filter((row, i, arr) => arr.slice(0, i).findIndex((l) => l.name === row.name) === -1)
  .toReversed();

answered Jan 2, 2024 at 10:16

You

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