How can I write a function that returns the objects in an array that have the two same property values?

Question

Let's say I have the following object:

const myObjects = [
    { name: "Alice", age: 30 },
    { name: "Bob", age: 25 },
    { name: "Alice", age: 30 },
    { name: "David", age: 25 }
];

I wrote the following function, so that the objects with the specified same props are returned in a new array:

function findObjectsWithSameProperties(objects, property1, property2) {
  // Create an empty array to store the results
  const matchingObjects = [];

  // Loop through each object in the array
  for (const obj of objects) {
    // Check if the object has both specified properties
    if (obj.hasOwnProperty(property1) && obj.hasOwnProperty(property2)) {
      // Check if the values of the specified properties are the same
      if (obj[property1] === obj[property2]) {
        // If they are, add the object to the results array
        matchingObjects.push(obj);
      }
    }
  }

  // Return the array of matching objects
  return matchingObjects;
}

However, my function isn't returning anything when I expect it to return this:

[
    { name: "Alice", age: 30 },
    { name: "Alice", age: 30 },
];

Here's how I'm calling the function: findObjectsWithSameProperties(myObjects, "age", "name");

Does anyone know what I'm doing wrong? Here's a CodePen link: https://codepen.io/obliviga/pen/WNWNbMX?editors=0011

Edit: I updated the codepen and it works now.

Answer 1

You're looping through objects, checking whether the object has both props and then checking whether the name === age. Furthermore you're checking the same object's properties so you won't find duplicates either. This will obviously never be true. I suggest adding a history of the ones you've already looped through and then comparing whether it has already seen the same object or not.

function findObjectsWithSameProperties(objects, property1, property2) {
  // Create an empty array to store the results
  const matchingObjects = [];
  const seen = {};
  
  // Loop through each object in the array
  for (const obj of objects) {
    // Check if the object has both specified properties
    if (obj.hasOwnProperty(property1) && obj.hasOwnProperty(property2)) {
      const key = obj[property1] + '-' + obj[property2];
      // Check if we have seen this combination before
      if (seen[key]) {
        // Increment if it already exists
        seen[key].count++;
        // Add the object to the array of matching objects
        seen[key].objects.push(obj);
      } else {
        // If it's the first time it's ever seen this object, set count to 1
        seen[key] = { count: 1, objects: [obj] };
      }
    }
  }

  
  for (const key in seen) {
    if (seen[key].count > 1) {
      matchingObjects.push(...seen[key].objects); 
//count essentially keeps track of how many times it's already seen that object. If there has been a duplicate, it pushes the objects your matchingObjects array.
    }
  }

  // Return the array of matching objects
  return matchingObjects;
}

Answer 2

try this :

const myObjects = [
    { name: "Alice", age: 30 },
    { name: "Bob", age: 25 },
    { name: "Alice", age: 30 },
    { name: "David", age: 25 }
];

const matchingObjects = (objectsArray,...properties) => objectsArray.filter( ( mainObject,index ) => 
    objectsArray.filter( ( obj,idx ) => idx != index ).some( object => 
        properties.every( prop => mainObject[prop] == object[prop] )));

console.log(matchingObjects(myObjects,"name"));

Answer 3

You can group objects by name and then filter the groups with length > 1 and flatten:

const myObjects = [
    { name: "Alice", age: 30 },
    { name: "Bob", age: 25 },
    { name: "Alice", age: 30 },
    { name: "David", age: 25 }
];

const grouped = {};
myObjects.forEach(obj => (grouped[obj.name] ??= []).push(obj))
const result = Object.values(grouped).filter(arr => arr.length > 1).flat();

console.log(result);

Answer 4

Updated my function as follows to return an array with the 2 same passed in properties:

function findObjectsWithSamePropertyValues(objects, property1, property2) {
    const result = [];
    
    for (let i = 0; i < objects.length; i++) {
        const obj1 = objects[i];
        
        for (let j = i + 1; j < objects.length; j++) {
            const obj2 = objects[j];
            
            if (obj1[property1] === obj2[property1] && obj1[property2] === obj2[property2]) {
                result.push(obj1, obj2);
            }
        }
    }
    
    return result;
}