How to compare object values in an array of objects?

Question

I am trying to compare an array of objects. Each object has the same keys, but varying values for each key. I would like to create a function that compares each object for similar key value pairs.

I only care about the quality and location keys for each object, and I want to compare all objects against these two keys.

For example, if the first and second object in the array of objects contains the same value for two keys, I would like to create an output array of objects that summarizes each grouping.

Explanation: Object one and two contain the same value for quality and location . Since the third object does not, a new object should be created that summarizes the information from the first and second objects. That new object should contains an array of all fruit names and and array of all tags. The output object is shown below.

// Input
data = [
  {
    id: '1',
    fruit: 'granny smith',
    quality: 'good',
    location: 'chicago',
    tags: ['green', 'sweet'],
  },
  {
    id: '2',
    fruit: 'Fuji',
    quality: 'good',
    location: 'chicago',
    tags: ['red', 'tart'],
  },
  {
    id: '3',
    fruit: 'gala',
    quality: 'bad',
    location: 'san diego',
    tags: ['tall', 'thin'],
  },
];

// Function
function compareObjects(arr) {
  const grouped = [];

  // Loop over every fruit
  const similarObjects = arr.filter((obj, id) => {
    // create structure for each common object
    let shape = {
      id,
      fruits: [],
      quality: '',
      tags: [],
    };

    arr.forEach((item) => {
      // Return a new shape object that contains all fruit names, tags, and quality
      if (item.quality == obj.quality && item.location == obj.location) {
        shape.id = id;
        shape.fruits.push(item.fruit);
        shape.fruits.push(obj.fruit);
        shape.quality = item.quality;
        shape.tags.push(item.tag);
        shape.tags.push(obj.tag);
        return shape;
      }
    });
    return obj;
  });

  return similarObjects;
}

console.log(compareObjects(data));

// Output
const output = [
  {
    id: 'a',
    fruits: ['grann smith', 'fuji'],
    quality: 'good',
    tags: ['green', 'sweet', 'red', 'tart'],
  },
  ...
];

Answer 1

You can group the data by their quality and location using Array.prototype.reduce and filter the groups where the length is greater than one.

 const data = [ { id: "1", fruit: "granny smith", quality: "good", location: "chicago", tags: ["green", "sweet"] }, { id: "2", fruit: "Fuji", quality: "good", location: "chicago", tags: ["red", "tart"] }, { id: "3", fruit: "gala", quality: "bad", location: "san diego", tags: ["tall", "thin"] }, ], output = Object.values( data.reduce((r, d) => { const key = `${d.quality}+${d.location}`; if (!r[key]) { r[key] = { id: d.id, fruits: [], quality: d.quality, location: d.location, tags: [] }; } r[key].fruits.push(d.fruit); r[key].tags.push(...d.tags); return r; }, {}) ).filter((d) => d.fruits.length > 1); console.log(output);

If you also wish to only keep unique fruits then you can map over the resultant array and remove the duplicates using a Set .

 const data = [ { id: "1", fruit: "granny smith", quality: "good", location: "chicago", tags: ["green", "sweet"] }, { id: "2", fruit: "Fuji", quality: "good", location: "chicago", tags: ["red", "tart"] }, { id: "3", fruit: "gala", quality: "bad", location: "san diego", tags: ["tall", "thin"] }, ], output = Object.values( data.reduce((r, d) => { const key = `${d.quality}+${d.location}`; if (!r[key]) { r[key] = { id: d.id, fruits: [], quality: d.quality, location: d.location, tags: [] }; } r[key].fruits.push(d.fruit); r[key].tags.push(...d.tags); return r; }, {}) ) .filter((d) => d.fruits.length > 1) .map((d) => ({ ...d, fruits: [...new Set(d.fruits)] })); console.log(output);

Other relevant documentations:

• Spread syntax (...)
• Array.prototype.push
• Array.prototype.filter
• Object.values