Javascript – How to remove all duplicates from an array of objects

arraysduplicatesjavascriptobject

I have an object that contains an array of objects.

things = new Object();

things.thing = new Array();

things.thing.push({place:"here",name:"stuff"});
things.thing.push({place:"there",name:"morestuff"});
things.thing.push({place:"there",name:"morestuff"});

I'm wondering what is the best method to remove duplicate objects from an array. So for example, things.thing would become…

{place:"here",name:"stuff"},
{place:"there",name:"morestuff"}

Best Answer

How about with some es6 magic?

things.thing = things.thing.filter((thing, index, self) =>
  index === self.findIndex((t) => (
    t.place === thing.place && t.name === thing.name
  ))
)

Reference URL

A more generic solution would be:

const uniqueArray = things.thing.filter((thing, index) => {
  const _thing = JSON.stringify(thing);
  return index === things.thing.findIndex(obj => {
    return JSON.stringify(obj) === _thing;
  });
});

Using the above property strategy instead of JSON.stringify:

const isPropValuesEqual = (subject, target, propNames) =>
  propNames.every(propName => subject[propName] === target[propName]);

const getUniqueItemsByProperties = (items, propNames) => 
  items.filter((item, index, array) =>
    index === array.findIndex(foundItem => isPropValuesEqual(foundItem, item, propNames))
  );

You can add a wrapper if you want the propNames property to be either an array or a value:

const getUniqueItemsByProperties = (items, propNames) => {
  const propNamesArray = Array.from(propNames);

  return items.filter((item, index, array) =>
    index === array.findIndex(foundItem => isPropValuesEqual(foundItem, item, propNamesArray))
  );
};

allowing both getUniqueItemsByProperties('a') and getUniqueItemsByProperties(['a']);

Stackblitz Example

Explanation

  • Start by understanding the two methods used:
  • Next take your idea of what makes your two objects equal and keep that in mind.
  • We can detect something as a duplicate, if it satisfies the criterion that we have just thought of, but it's position is not at the first instance of an object with the criterion.
  • Therefore we can use the above criterion to determine if something is a duplicate.
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