Generating arrays of duplicate elements in JavaScript

Question

Generating arrays of duplicate elements in JavaScript

Let's say we have an array structured like this:

let arr = [{
    name: "Peter"
}, {
    name: "Peter"
}, {
    name: "John"
}, {
    name: "Peter"
}, {
    name: "Sarah"
}, {
    name: "John"
}]

The goal is to transform it into a new array that groups the duplicates together like this:

let dupArray = [
    [{
        name: "Peter"
    }, {
        name: "Peter"
    }, {
        name: "Peter"
    }],
    [{
        name: "John"
    }, {
        name: "John"
    }],
    [{
        name: "Sarah"
    }]
]

This process focuses on creating a new array by grouping the duplicate elements, not simply duplicating them.

javascript arrays

Answer 1

Answer №1

Convert the array into a Map and retrieve the values:

const data = [{
  name: "Alice"
}, {
  name: "Alice"
}, {
  name: "Bob"
}, {
  name: "Alice"
}, {
  name: "Eve"
}, {
  name: "Bob"
}];

const duplicatesArray = 
    [...data.reduce((accumulator, current) => 
        accumulator.set(current.name , (accumulator.get(current.name) || []).concat(current)),
     new Map()).values()];

console.log(duplicatesArray);

Answer 2

Convert the array into a Map and retrieve the values:

const data = [{
  name: "Alice"
}, {
  name: "Alice"
}, {
  name: "Bob"
}, {
  name: "Alice"
}, {
  name: "Eve"
}, {
  name: "Bob"
}];

const duplicatesArray = 
    [...data.reduce((accumulator, current) => 
        accumulator.set(current.name , (accumulator.get(current.name) || []).concat(current)),
     new Map()).values()];

console.log(duplicatesArray);

Answer 3

Answer №2

let names = [{name: "Peter"},{name: "Peter"},{name: "John"},{name: "Peter"},{name: "Sarah"},{name: "John"}]

  let groupNames = function(array){
      // counts the occurrences of each name
      let countMap = {};
      for(item of array){
          if(countMap[item.name] !== undefined){
              countMap[item.name]++;
          }
          else {
              countMap[item.name] = 1;
          }
      }

      // create desired format
      let formattedArray = [];
      for(name in countMap){
          let occurrenceCount = countMap[name];
          let subArray = [];
          for(let i = 0; i < occurrenceCount; i++){
              subArray.push({ "name" : name });
          }
          formattedArray.push(subArray);
      }

      return formattedArray;
  }

  document.getElementById("result").innerHTML = JSON.stringify(groupNames(names));

<pre id="result"></pre>

The groupNames function first counts the number of occurrences of each name, then generates a new representation by adding objects with the corresponding names based on the counts. The naming convention is arbitrary.

Answer 4

let names = [{name: "Peter"},{name: "Peter"},{name: "John"},{name: "Peter"},{name: "Sarah"},{name: "John"}]

  let groupNames = function(array){
      // counts the occurrences of each name
      let countMap = {};
      for(item of array){
          if(countMap[item.name] !== undefined){
              countMap[item.name]++;
          }
          else {
              countMap[item.name] = 1;
          }
      }

      // create desired format
      let formattedArray = [];
      for(name in countMap){
          let occurrenceCount = countMap[name];
          let subArray = [];
          for(let i = 0; i < occurrenceCount; i++){
              subArray.push({ "name" : name });
          }
          formattedArray.push(subArray);
      }

      return formattedArray;
  }

  document.getElementById("result").innerHTML = JSON.stringify(groupNames(names));

<pre id="result"></pre>

The groupNames function first counts the number of occurrences of each name, then generates a new representation by adding objects with the corresponding names based on the counts. The naming convention is arbitrary.

Generating arrays of duplicate elements in JavaScript

Answer №1

Answer №2

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