TIL Eliminating duplicate objects

POSTED ON: Jul 30, 2021

TAGS: javascript

Using Set datatypes can let you do this with no fuss.

const values = ['jane', 'lars', 'jane'];
const uniqueValues = [...new Set(values)]; // ['jane', 'lars'];

But you can't do this with arrays that have objects inside of it.

Set would consider each object to be unique.

const members = [
  {
    first: 'Jane',
    last: 'Bond',
    id: '10yejma',
  },
  {
    first: 'Lars',
    last: 'Croft',
    id: '1hhs0k2',
  },
  {
    first: 'Jane',
    last: 'Bond',
    id: '1y15hhu',
  },
];

Solutions would be to:

Approach 1: Building a new Array without duplicates #

You can create a helper function that compares a specific key, and add them only if they don't exist.

const uniqueMembers1 = [];

for (const m of members) {
  if (!containsMember(uniqueMembers1, m)) {
    uniqueMembers1.push(m);
  }
}

function containsMember(memberArray, member) {
  return memberArray.find(
    (m) => m.first === member.first && m.last === member.last);
}

Approach #2: using filter #

// Only keep members m if they appear for the first time
const uniqueMembers2 = members.filter(
  (m, index, ms) => getIndexOfMember(ms, m) === index);

function getIndexOfMember(memberArray, member) {
  return memberArray.findIndex(
    (m) => m.first === member.first && m.last === member.last);
}

Approach #3: Map from unique keys to members #

const uniqueKeyToMember = new Map(
  members.map(m => [m.first+'\t'+m.last, m])); // [key, value]

const uniqueMembers3 = [...uniqueKeyToMember.values()];

Via Eliminating duplicate objects: three approaches

Related TILs

Tagged: javascript

• Next: TIL how devs can explain what needs to happenIf we’re attempting to convince someone to try something, we should try to empathize with the people we’re presenting to.
• Previous: TIL combining PHP arraysarray_merge, array_replace, and the (+) union operator