Nested Reduce with values in JS

Question

Good morning, after an array.map I have an array containing the same assignments with some nested ratings:

const assignments = [
    {
      name: "assignmentOne",
      difficultyRating: 1,
      funRating: 2
    },
    {
      name: "assignmentOne",
      difficultyRating: 3,
      funRating: 4
    },
    {
      name: "assignmentOne",
      difficultyRating: 5,
      funRating: 1
    }
]

Now I would like to get the total difficulty/fun rating, which would look like one of the following:

//Both the difficulty and fun rating in the same record
const assignmentsTotal = [
    {
      name: "assignmentOne",
      totalDifficultyRating: 9,
      totalFunRating: 7
    }
]

//Difficulty and fun rating as separate records
const assignmentsDifficultyTotal = [
    {
      name: "assignmentOne",
      totalDifficultyRating: 9
    }
]
const assignmentsFunTotal = [
    {
      name: "assignmentOne",
      totalFunRating: 7
    }
]

I'm pretty confident the best way to do this is using the reduce method. After some digging around the only thing that came close to what I want to achieve is the following article, yet I'm not able to get this to work properly. Is there a good way to do this from the starting point above, or would it be better to create separate arrays using array.map and after use the reduce method?

Hello, @ZeeAars! What code have you tried so far? Much like an educational setting, we prefer questions that show you work. — rxgx
– rxgx, Commented Dec 7, 2020 at 9:09
I totally forgot adding what I had tried so far, as I was trying to formulate my question as good as possible, my bad man. So far I had tried using forEach to go one level deeper and making new sets/arrays(using .map) of the data provided above, tho everything I tried either returned nan or undefined. Which I thought had something to do with all assignments having a unique name(data is a mockup JSON with 10 students with 56 assignments, all of them with a fun and difficulty rating) I will not forget to add my tests next time I want to ask a question and can still add some if you want — ZeeAars
– ZeeAars, Commented Dec 7, 2020 at 9:38

Kuldeep Bora · Accepted Answer · 2020-12-07 09:03:42Z

0

If you are looking for same 'name' objects in array, below should be ok:

const reducer = assignments.reduce((total, current) => {
    return { name: current.name, difficultyRating : total.difficultyRating + current.difficultyRating, funRating : total.funRating + current.funRating } });

if you want to group objects by name, then look at lodash groupby function. In general, lodash is very handy in all array/obj functionalities.

answered Dec 7, 2020 at 9:03

Kuldeep Bora

5,0403 gold badges16 silver badges17 bronze badges

Sign up to request clarification or add additional context in comments.

7 Comments

rxgx Over a year ago

I think you forgot to set the initial value of the accumulator for the total argument.

ZeeAars Over a year ago

This worked perfectly, thanks a bunch man, both for the swift response and really clean answer :D

secan Over a year ago

This solution works only if you have just one assignment (e.g. assignmentOne) but if you have more assignments (e.g. assignmentOne and assignmentTwo) it will sum the ratings of all assignments and use as name the one of the last assignment.

ZeeAars Over a year ago

it worked with my array of 56 different assignments, all of them kept their original name and structure, so I'm not sure what you mean @secan

secan Over a year ago

@ZeeAars, I created a code snippet to show what I mean here: jsfiddle.net/j014c67y.

|

secan · Accepted Answer · 2020-12-07 09:20:44Z

const assignments = [{
    name: "assignmentOne",
    difficultyRating: 1,
    funRating: 2
  },
  {
    name: "assignmentOne",
    difficultyRating: 3,
    funRating: 4
  },
  {
    name: "assignmentOne",
    difficultyRating: 5,
    funRating: 1
  },
  {
    name: "assignmentTwo",
    difficultyRating: 5,
    funRating: 3
  },
  {
    name: "assignmentTwo",
    difficultyRating: 5,
    funRating: 1
  }
];

// if you want the totals as an array:
const assignmentsTotalArray = assignments.reduce((totalArr, item) => {
  // check whether the assignment is already in the array
  const assignmentIndex = totalArr.findIndex(elem => elem.name === item.name);

  // if the assignment is not in the array, add it and initialize the totals
  // otherwise update the totals
  if (assignmentIndex === -1) {
    totalArr.push({
      name: item.name,
      totalDifficultyRating: item.difficultyRating,
      totalFunRating: item.funRating
    });
  } else {
    totalArr[assignmentIndex].totalDifficultyRating += item.difficultyRating;
    totalArr[assignmentIndex].totalFunRating += item.funRating;
  }

  return totalArr;
}, []);

console.log('### assignmentsTotalArray:');
console.log(assignmentsTotalArray);

// if you want the totals as an object:
const assignmentsTotalObject = assignments.reduce((totalObj, item) => {
  // if the output object already contains the assignment, sum the ratings
  // otherwise create a new key for the assignment and initialize the ratings
  if (totalObj[item.name]) {
    totalObj[item.name].totalDifficultyRating += item.difficultyRating;
    totalObj[item.name].totalFunRating += item.funRating;
  } else {
    totalObj[item.name] = {
      totalDifficultyRating: item.difficultyRating,
      totalFunRating: item.funRating
    };
  }

  return totalObj;
}, {});

console.log('### assignmentsTotalObject:')
console.log(assignmentsTotalObject);

Collectives™ on Stack Overflow

Nested Reduce with values in JS

2 Answers 2

7 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

7 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related