removing duplicate objects from an array

Question

I have been working on removing duplicate objects in an array. I keep getting an error on trying to read the filterList[i+1].tagID. I can manually enter the [i+1] values and get the correct results. I'm not sure why the i+1 is an issue. I have also wondered if if it better to use a slice[i, 1] than the delete.

const filterList = [{
  tagID: 1,
  tagName: "Red"
}, {
  tagID: 1,
  tagName: "Red"
}, {
  tagID: 2,
  tagName: "Orange"
}, {
  tagID: 2,
  tagName: "Orange"
}, {
  tagID: 5,
  tagName: "Blue"
}, {
  tagID: 5,
  tagName: "Blue"
}, {
  tagID: 5,
  tagName: "Blue"
}, {
  tagID: 6,
  tagName: "Indigo"
}, {
  tagID: 6,
  tagName: "Indigo"
}, {
  tagID: 7,
  tagName: "Violet"
}, {
  tagID: 7,
  tagName: "Violet"
}, {
  tagID: 7,
  tagName: "Violet"
}]

filterList.sort(function(a, b) {
  return a.tagID - b.tagID;
});

for (let i = 0; i < filterList.length; i++) {
  if (filterList[i].tagId == filterList[i+1].tagID) {
    delete filterList[i];
  }
}

console.log(filterList)

developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/… — Joe
– Joe, Commented Jun 6, 2018 at 21:01
Changed loop till filterList.length - 1 for (let i = 0; i < filterList.length-1; i++) { if (filterList[i].tagId == filterList[i+1].tagID) { delete filterList[i]; } } — Mohsin Mehmood
– Mohsin Mehmood, Commented Jun 6, 2018 at 21:02

baao · Accepted Answer · 2018-06-06 21:30:59Z

3

Try this! Using filter and es2015

const filterListResult = filterList.filter((item, index, self) => index === self.findIndex((t) => (t.tagID === item.tagID && t.tagName === item.tagName)));
console.log(filterListResult);

<script>
const filterList = [{
  tagID: 1,
  tagName: "Red"
}, {
  tagID: 1,
  tagName: "Red"
}, {
  tagID: 2,
  tagName: "Orange"
}, {
  tagID: 2,
  tagName: "Orange"
}, {
  tagID: 5,
  tagName: "Blue"
}, {
  tagID: 5,
  tagName: "Blue"
}, {
  tagID: 5,
  tagName: "Blue"
}, {
  tagID: 6,
  tagName: "Indigo"
}, {
  tagID: 6,
  tagName: "Indigo"
}, {
  tagID: 7,
  tagName: "Violet"
}, {
  tagID: 7,
  tagName: "Violet"
}, {
  tagID: 7,
  tagName: "Violet"
}]
</script>

edited Jun 6, 2018 at 21:30

baao

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answered Jun 6, 2018 at 21:15

Henrique Viana

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Comments

zfrisch · Accepted Answer · 2018-06-06 21:21:03Z

You can use the set object to remove duplicate IDs, then use map and find functions to mutate the result to give you only the first appearance of each tagID.

 Array.from(new Set(filterList.map(_=> _.tagID)))
  .map(ID=> filterList.find(o=> o.tagID === ID)));

const filterList = [{
  tagID: 1,
  tagName: "Red"
}, {
  tagID: 1,
  tagName: "Red"
}, {
  tagID: 2,
  tagName: "Orange"
}, {
  tagID: 2,
  tagName: "Orange"
}, {
  tagID: 5,
  tagName: "Blue"
}, {
  tagID: 5,
  tagName: "Blue"
}, {
  tagID: 5,
  tagName: "Blue"
}, {
  tagID: 6,
  tagName: "Indigo"
}, {
  tagID: 6,
  tagName: "Indigo"
}, {
  tagID: 7,
  tagName: "Violet"
}, {
  tagID: 7,
  tagName: "Violet"
}, {
  tagID: 7,
  tagName: "Violet"
}]

let result = Array.from(new Set(filterList.map(_ => _.tagID))).map((ID, index) => filterList.find(o => o.tagID == ID));

console.log(result);

Nina Scholz · Accepted Answer · 2018-06-06 21:06:48Z

You could start the iteration from index 1 and check the last element with the actual element.

const filterList = [{ tagID: 1, tagName: "Red" }, { tagID: 1, tagName: "Red" }, { tagID: 2, tagName: "Orange" }, { tagID: 2, tagName: "Orange" }, { tagID: 5, tagName: "Blue" }, { tagID: 5, tagName: "Blue" }, { tagID: 5, tagName: "Blue" }, { tagID: 6, tagName: "Indigo" }, { tagID: 6, tagName: "Indigo" }, { tagID: 7, tagName: "Violet" }, { tagID: 7, tagName: "Violet" }, { tagID: 7, tagName: "Violet" }]

filterList.sort(function(a, b) {
    return a.tagID - b.tagID;
});

for (let i = 1; i < filterList.length; i++) {
    if (filterList[i - 1].tagId === filterList[i].tagID) {
        delete filterList[i];
    }
}

console.log(filterList);

Jean · Accepted Answer · 2018-06-06 23:14:52Z

2

Generate a new list using reduce:

const filterList = [{ tagID: 1, tagName: "Red" }, { tagID: 1, tagName: "Red" }, { tagID: 2, tagName: "Orange" }, { tagID: 2, tagName: "Orange" }, { tagID: 5, tagName: "Blue" }, { tagID: 5, tagName: "Blue" }, { tagID: 5, tagName: "Blue" }, { tagID: 6, tagName: "Indigo" }, { tagID: 6, tagName: "Indigo" }, { tagID: 7, tagName: "Violet" }, { tagID: 7, tagName: "Violet" }, { tagID: 7, tagName: "Violet" }]

const newList = filterList.reduce((total, current) => {
    const exist = total.some(t => t.tagID === current.tagID)
    if (!exist) {
        total.push(current)
    }
    return total
}, [])

edited Jun 6, 2018 at 23:14

answered Jun 6, 2018 at 21:17

Jean

3012 silver badges8 bronze badges

2 Comments

Jeff Winkler Over a year ago

You lost me on "actual". Where does this come from?

Jean Over a year ago

sorry I had called the current variable from actual before and forgot to replace it later

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