Select only distinct values from the array

Question

Select only distinct values from the array

Is there an efficient way to filter arrays for objects with unique values in a specific field, rather than just unique values overall?

Consider having an array like [obj1, obj2, obj3, ...], where each object follows this structure:

{
firstName: "...",
lastName: "..."
}

What's the best approach to filter out objects based on uniqueness of their first names? It would be great if it could be a concise one-liner without sacrificing readability.

javascript arrays filter

Answer 1

Answer №1

Include only the items that have not been previously found in the given array. The definition of cond determines whether two items are considered "equal".

function filterUniqueItems(a, cond) {
  return a.filter((element, index) => a.findIndex(e2 => cond(element, e2)) === index);
}

const sampleArray = [
  { firstname: "John", lastname: "Doe" },
  { firstname: "Jane", lastname: "Doe" },
  { firstname: "John", lastname: "Smith" }
];

console.log(filterUniqueItems(sampleArray, (object1, object2) => object1.firstname === object2.firstname));

Answer 2

Include only the items that have not been previously found in the given array. The definition of cond determines whether two items are considered "equal".

function filterUniqueItems(a, cond) {
  return a.filter((element, index) => a.findIndex(e2 => cond(element, e2)) === index);
}

const sampleArray = [
  { firstname: "John", lastname: "Doe" },
  { firstname: "Jane", lastname: "Doe" },
  { firstname: "John", lastname: "Smith" }
];

console.log(filterUniqueItems(sampleArray, (object1, object2) => object1.firstname === object2.firstname));

Answer 3

Answer №2

To condense the array into a Map, and then spread the map values back to an array, follow these steps:

If you prefer to retain the first encountered objects, ensure the map does not already contain the key "firstName" before setting it again.

const arr = [{"firstname":"Robert","lastname":"Smith"},{"firstname":"Francis","lastname":"Collins"},{"firstname":"Robert","lastname":"Ludlum"},{"firstname":"Francis","lastname":"bacon"}];
              
const result = [...arr.reduce((map, obj) => map.has(obj.firstname) ? map : map.set(obj.firstname, obj), new Map()).values()];

console.log(result);

If you want to keep the last objects without checking for duplicates, simply set them directly:

const arr = [{"firstname":"Robert","lastname":"Smith"},{"firstname":"Francis","lastname":"Collins"},{"firstname":"Robert","lastname":"Ludlum"},{"firstname":"Francis","lastname":"bacon"}];

const result = [...arr.reduce((map, obj) => map.set(obj.firstname, obj), new Map()).values()];

console.log(result);

Answer 4

To condense the array into a Map, and then spread the map values back to an array, follow these steps:

If you prefer to retain the first encountered objects, ensure the map does not already contain the key "firstName" before setting it again.

const arr = [{"firstname":"Robert","lastname":"Smith"},{"firstname":"Francis","lastname":"Collins"},{"firstname":"Robert","lastname":"Ludlum"},{"firstname":"Francis","lastname":"bacon"}];
              
const result = [...arr.reduce((map, obj) => map.has(obj.firstname) ? map : map.set(obj.firstname, obj), new Map()).values()];

console.log(result);

If you want to keep the last objects without checking for duplicates, simply set them directly:

const arr = [{"firstname":"Robert","lastname":"Smith"},{"firstname":"Francis","lastname":"Collins"},{"firstname":"Robert","lastname":"Ludlum"},{"firstname":"Francis","lastname":"bacon"}];

const result = [...arr.reduce((map, obj) => map.set(obj.firstname, obj), new Map()).values()];

console.log(result);

Answer 5

Answer №3

To achieve this, you can utilize the reduce method and initialize the value as an array. Then, conditionally push objects to a new array if a certain condition is met, such as checking if the first name already exists:

var arr = [ { firstname: "John",
              lastname: "Doe" },
            { firstname: "Jane",
              lastname: "Doe" },
            { firstname: "John",
              lastname: "Doe" }];
             
console.log(
  arr.reduce(
    function(unique_arr, obj) {
      if(!unique_arr.some(x => x.firstname === obj.firstname)) {
        unique_arr.push(obj)
      }
      return unique_arr; 
    }, [])
);

Answer 6

To achieve this, you can utilize the reduce method and initialize the value as an array. Then, conditionally push objects to a new array if a certain condition is met, such as checking if the first name already exists:

var arr = [ { firstname: "John",
              lastname: "Doe" },
            { firstname: "Jane",
              lastname: "Doe" },
            { firstname: "John",
              lastname: "Doe" }];
             
console.log(
  arr.reduce(
    function(unique_arr, obj) {
      if(!unique_arr.some(x => x.firstname === obj.firstname)) {
        unique_arr.push(obj)
      }
      return unique_arr; 
    }, [])
);

Answer 7

Answer №4

When looking for unique values in an array, it is common to check if the result array contains a value. However, I prefer using an object approach where the value is always set without needing to check for uniqueness. This method works under the assumption that objects can only have unique keys:

var arr = [{
    firstName: "Amy",
    lastName: "Adams"
  },
  {
    firstName: "Bryan",
    lastName: "Heart"
  },
  {
    firstName: "Amy",
    lastName: "Adams"
  }
];


var unique = {};

for (var i = 0, n = arr.length; i < n; i++) {
  // Key is your unique condition
  var key = [arr[i].firstName, arr[i].lastName].join(' ');
  unique[key] = arr[i];
}

console.log('Keys:', Object.keys(unique));     // only shown for simplicity
console.log('Values:', Object.values(unique));

Answer 8

When looking for unique values in an array, it is common to check if the result array contains a value. However, I prefer using an object approach where the value is always set without needing to check for uniqueness. This method works under the assumption that objects can only have unique keys:

var arr = [{
    firstName: "Amy",
    lastName: "Adams"
  },
  {
    firstName: "Bryan",
    lastName: "Heart"
  },
  {
    firstName: "Amy",
    lastName: "Adams"
  }
];


var unique = {};

for (var i = 0, n = arr.length; i < n; i++) {
  // Key is your unique condition
  var key = [arr[i].firstName, arr[i].lastName].join(' ');
  unique[key] = arr[i];
}

console.log('Keys:', Object.keys(unique));     // only shown for simplicity
console.log('Values:', Object.values(unique));

Answer 9

Answer №5

What do you think of this 2-liner challenge?

var arr = [{name: 'John'}, {name: 'Jane'}, {name: 'Jane'}];

var names = [];
var uniqueNames = arr.filter(obj =>
  names.indexOf(obj.name) > -1
      ? false : names.push(obj.name))
console.log( JSON.stringify(uniqueNames));

Answer 10

What do you think of this 2-liner challenge?

var arr = [{name: 'John'}, {name: 'Jane'}, {name: 'Jane'}];

var names = [];
var uniqueNames = arr.filter(obj =>
  names.indexOf(obj.name) > -1
      ? false : names.push(obj.name))
console.log( JSON.stringify(uniqueNames));

Answer 11

Answer №6

To ensure that only unique first names are stored, I employ a filtering mechanism and maintain a Set of those that have already been encountered:

 const uniqueFirstNames = new Set();

 const filteredResult = array.filter(({ firstName }) => !uniqueFirstNames.has(firstName) && uniqueFirstNames.add(firstName));

Answer 12

To ensure that only unique first names are stored, I employ a filtering mechanism and maintain a Set of those that have already been encountered:

 const uniqueFirstNames = new Set();

 const filteredResult = array.filter(({ firstName }) => !uniqueFirstNames.has(firstName) && uniqueFirstNames.add(firstName));

Select only distinct values from the array

Answer №1

Answer №2

Answer №3

Answer №4

Answer №5

Answer №6

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