Restructring array of objects

Question

I've been struggling to restructure this particular object;

[
  {
    "userId": 1,
    "name": "Breaker of Sky",
    "rank": 1
  },
  {
    "userId": 1,
    "name": "Slayer of Mountain",
    "rank": 2
  },
  {
    "userId": 1,
    "name": "Balthromaw",
    "rank": 3
  },
  {
    "userId": 1,
    "name": "Death",
    "rank": -1
  },
  {
    "userId": 3,
    "name": "Breaker of Sky",
    "rank": 2
  },
  {
    "userId": 3,
    "name": "Slayer of Mountain",
    "rank": 3
  },
  {
    "userId": 3,
    "name": "Balthromaw",
    "rank": 1
  },
  {
    "userId": 3,
    "name": "Death",
    "rank": -1
  },
  {
    "userId": 4,
    "name": "Breaker of Sky",
    "rank": 3
  },
  {
    "userId": 4,
    "name": "Slayer of Mountain",
    "rank": 2
  },
  {
    "userId": 4,
    "name": "Balthromaw",
    "rank": 1
  },
  {
    "userId": 4,
    "name": "Death",
    "rank": -1
  },
  {
    "userId": 8,
    "name": "Breaker of Sky",
    "rank": 2
  },
  {
    "userId": 8,
    "name": "Slayer of Mountain",
    "rank": 3
  },
  {
    "userId": 8,
    "name": "Balthromaw",
    "rank": 4
  },
  {
    "userId": 8,
    "name": "Death",
    "rank": 1
  }
]

to make it look like this object below.

[
     { ranking: [['Death'], ['Breaker of Sky'], ['Slayer of Mountain'], ['Balthromaw']], count: 2 },
     { ranking: [['Death'], ['Balthromaw'], ['Breaker of Sky'], ['Slayer of Mountain']], count: 1 },
     { ranking: [['Death'], ['Balthromaw'], ['Slayer of Mountain'], ['Breaker of Sky']], count: 1 },
]

To simply explain the process, we first need to look for the userId's and group the names with ranks which have same userId's. Then it should line up the names by looking their ranks (-1 will always be at the first place). After that, we should look for the sequence, count it and write down. As an example, this sequence, [['Death'], ['Breaker of Sky'], ['Slayer of Mountain'], ['Balthromaw']] , has been found 2 times and therefore count is 2.

I would appreciate your help regarding this problem.

My code:

Here is what I have done so far. It's still missing the lining up part of the names by sorting ranks and also values of the ranking property are not arrays. Additionally, I couldn't do the count of sequence part too. Could you help me out with it?

const merged = data.reduce((r, { userId, ...rest }) => {
  const key = `${userId}`;
  r[key] = r[key] || { ranking: [] };
  r[key]['ranking'].push(rest);
  return r;
}, {});

const rankArray = Object.values(merged);
console.log(rankArray);

The output I get:

[
  {
    "ranking": [
      {
        "name": "Breaker of Sky",
        "rank": 1
      },
      {
        "name": "Slayer of Mountain",
        "rank": 2
      },
      {
        "name": "Balthromaw",
        "rank": 3
      },
      {
        "name": "Death",
        "rank": -1
      }
    ]
  },
  {
    "ranking": [
      {
        "name": "Breaker of Sky",
        "rank": 2
      },
      {
        "name": "Slayer of Mountain",
        "rank": 3
      },
      {
        "name": "Balthromaw",
        "rank": 1
      },
      {
        "name": "Death",
        "rank": -1
      }
    ]
  },
  {
    "ranking": [
      {
        "name": "Breaker of Sky",
        "rank": 3
      },
      {
        "name": "Slayer of Mountain",
        "rank": 2
      },
      {
        "name": "Balthromaw",
        "rank": 1
      },
      {
        "name": "Death",
        "rank": -1
      }
    ]
  },
  {
    "ranking": [
      {
        "name": "Breaker of Sky",
        "rank": 2
      },
      {
        "name": "Slayer of Mountain",
        "rank": 3
      },
      {
        "name": "Balthromaw",
        "rank": 4
      },
      {
        "name": "Death",
        "rank": 1
      }
    ]
  }
]

ggorlen · Accepted Answer · 2022-01-05 21:04:12Z

1

There's a few steps to do:

Group by userId, which you've already done.
Sort the values for each user by rank.
Build a map of counts for each array of ranking items. I'm assuming the ranking numbers don't matter, only the string names.
Prune any extra elements with count > 1 in the map. (I think this is the logic you want; if it isn't, you can remove the delete byUser[userId] line)
Iterate and attach the final counts to each object in the result array.

Here's one approach to all of this:

const data = [ { "userId": 1, "name": "Breaker of Sky", "rank": 1 }, { "userId": 1, "name": "Slayer of Mountain", "rank": 2 }, { "userId": 1, "name": "Balthromaw", "rank": 3 }, { "userId": 1, "name": "Death", "rank": -1 }, { "userId": 3, "name": "Breaker of Sky", "rank": 2 }, { "userId": 3, "name": "Slayer of Mountain", "rank": 3 }, { "userId": 3, "name": "Balthromaw", "rank": 1 }, { "userId": 3, "name": "Death", "rank": -1 }, { "userId": 4, "name": "Breaker of Sky", "rank": 3 }, { "userId": 4, "name": "Slayer of Mountain", "rank": 2 }, { "userId": 4, "name": "Balthromaw", "rank": 1 }, { "userId": 4, "name": "Death", "rank": -1 }, { "userId": 8, "name": "Breaker of Sky", "rank": 2 }, { "userId": 8, "name": "Slayer of Mountain", "rank": 3 }, { "userId": 8, "name": "Balthromaw", "rank": 4 }, { "userId": 8, "name": "Death", "rank": 1 } ];

const byUser = data.reduce((a, e) => {
  a[e.userId] = a[e.userId] || [];
  a[e.userId].push(e);
  return a;
}, {});
const counts = {};

for (const [userId, ranking] of Object.entries(byUser)) {
  ranking.sort((a, b) => a.rank - b.rank);
  byUser[userId] = ranking.map(e => e.name);
  const k = byUser[userId];
  counts[k] = ++counts[k] || 1;
  
  if (counts[k] > 1) {
    delete byUser[userId];
  }
}

const result = Object.values(byUser).map(v => ({
  ranking: v,
  count: counts[v],
}));
console.log(result);

edited Jan 5, 2022 at 21:04

answered Jan 5, 2022 at 20:56

ggorlen

59.4k8 gold badges119 silver badges173 bronze badges

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

2 Comments

Rasqo Over a year ago

Wow, you are amazing! That's exactly what I wanted however I just want one more thing which is that each value of ranking should be in an array of arrays like here you can see below ; { ranking: [['Death'], ['Breaker of Sky'], ['Slayer of Mountain'], ['Balthromaw']], count: 2 } How can I do it? Thanks in advance!

ggorlen Over a year ago

Oh, I missed that requirement. I'd keep it 1-d, but if you need those 1-element inner arrays for some reason it's pretty simple: use ranking: v.map(e => [e]) inside the final map instead of ranking: v.

Collectives™ on Stack Overflow

Restructring array of objects

1 Answer 1

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related