CODEWITHSUNDEEP
javascriptarrays
Marian Sandur
Marian Sandur

Reputation: 73

Find elements in array of objects that have same properties and create a new array of objects

I have an array of objects like this:

arr = [
  { a: "dog", b: 8, c: "male", d: "big", e: 100 },
  { a: "dog1", b: 5, c: "female", d: "big", e: 200},
  { a: "dog2", b: 18, c: "female", d: "big", e: 350},
  { a: "dog2", b: 18, c: "female", d: "big", e: 350},
  { a: "dog", b: 3, c: "male", d: "big", e: 100 },
  { a: "dog", b: 8, c: "male", d: "big", e: 100 },
];

I want to create a new array containing only the property a and the sum of e of those objects that have the same values for b, c and d, so that I'll have and array like this:

arr2 = [
  { a: "dog", e: 300 },
  { a: "dog2", e: 700},
];

I've already tried to use a map function inside a map function looking for the elements that have the same properties b, c and d, then pushing the result in the arr2, but it pushes every time all the objects of my initial arr.

Upvotes: 1

Views: 1950

Answers (2)

Yevhen Horbunkov
Yevhen Horbunkov

Reputation: 15530

Universal solution for arbitrary array and keys to summarize

If you're looking for vanilla JS solution (no lodash), you may come up with something, adjustable to arbitrary group key property and property to summarize with Array.prototype.reduce():

  • build the Map, having desired property as a key;
  • increment Map items, based on the matching key
  • get Map.prototype.values() of that Map into array

const src = [
  { a: "dog", b: 8, c: "male", d: "big", e: 100 },
  { a: "dog1", b: 5, c: "female", d: "big", e: 200},
  { a: "dog2", b: 18, c: "female", d: "big", e: 350},
  { a: "dog2", b: 18, c: "female", d: "big", e: 350},
  { a: "dog", b: 3, c: "male", d: "big", e: 100 },
  { a: "dog", b: 8, c: "male", d: "big", e: 100 },
]

const summarizeValueByKey = (arr, key, val) => 
  [...arr
    .reduce((acc,{[key]: keyProp, [val]: valProp}) => {
      const group = acc.get(keyProp)
      group
        ? group[val] += valProp
        : acc.set(keyProp, {[key]: keyProp, [val]: valProp})
      return acc
    }, new Map)
    .values()]
    
console.log(summarizeValueByKey(src, 'a', 'e'))

Upvotes: 1

Terry Lennox
Terry Lennox

Reputation: 30675

You could use Array.reduce to create a map of the array elements, using b,c and d combined as the key.

Once we have this map, we can use Object.values() to get an array as the desired result.

arr = [
  { a: 'dog', b: 8, c: 'male', d: 'big', e: 100 },
  { a: 'dog1', b: 5, c: 'female', d: 'big', e: 200},
  { a: 'dog2', b: 18, c: 'female', d: 'big', e: 350},
  { a: 'dog2', b: 18, c: 'female', d: 'big', e: 350},
  { a: 'dog', b: 3, c: 'male', d: 'big', e: 100 },
  { a: 'dog', b: 8, c: 'male', d: 'big', e: 100 },
];

const result = Object.values(arr.reduce((acc, cur) => {
    // Create a key from b,c,d..
    const key = cur.b + cur.c + cur.d
    acc[key] = acc[key] || { a: cur.a, e: 0 };
    acc[key].e += cur.e;
    return acc;
}, {}))

console.log('Result:', result);

Upvotes: 3

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