Javascript -> Adding up values of nested objects with the same name

Question

I'm trying to calculate the total point scored per player per question.

For each question, I'm retrieving the data in the following format.

[
  {
    "_id":"5ab24e5e49e0f20a06d73ab7",
    "player":"Kareltje",
    "answers":
    [
      {
        "_id":"5ab227cf07818240934b11a5",
        "player":"Peter",
        "comment":"",
        "points":7,
        "__v":0
      },
      {
        "_id":"5ab24bf3b8494c76fd0bb31a",
        "player":"André",
        "comment":"",
        "points":6,
        "__v":0
      },
      {
        "_id":"5ab24bf7b8494c76fd0bb31b",
        "player":"Maikel",
        "comment":"",
        "points":5,
        "__v":0
      },
      {
        "_id":"5ab24bfab8494c76fd0bb31c",
        "player":"Iebele",
        "comment":"",
        "points":4,
        "__v":0
      },
      {
        "_id":"5ab24bfeb8494c76fd0bb31d",
        "player":"Bettina",
        "comment":"",
        "points":3,
        "__v":0
      },
      {
        "_id":"5ab24c01b8494c76fd0bb31e",
        "player":"Shirley",
        "comment":"",
        "points":2,
        "__v":0
      },
      {
        "_id":"5ab24c04b8494c76fd0bb31f",
        "player":"Suzanne",
        "comment":"",
        "points":1,
        "__v":0
      }
    ],
    "question":1,"__v":0
  },
  {
    "_id":"5ab24fa21e7caa1132720e7a",
    "player":"Maikel",
    "answers":
    [
      {
        "_id":"5ab24c04b8494c76fd0bb31f",
        "player":"Suzanne",
        "comment":"",
        "points":7,
        "__v":0
      },
      {
        "_id":"5ab24bfab8494c76fd0bb31c",
        "player":"Iebele",
        "comment":"",
        "points":6,
        "__v":0
      },
      {
        "_id":"5ab24bf3b8494c76fd0bb31a",
        "player":"André",
        "comment":"",
        "points":5,
        "__v":0
      },
      {
        "_id":"5ab24c01b8494c76fd0bb31e",
        "player":"Shirley",
        "comment":"",
        "points":4,
        "__v":0
      },
      {
        "_id":"5ab24bf7b8494c76fd0bb31b",
        "player":"Maikel",
        "comment":"",
        "points":3,
        "__v":0
      },
      {
        "_id":"5ab24bfeb8494c76fd0bb31d",
        "player":"Bettina",
        "comment":"",
        "points":2,
        "__v":0
      },
      {
        "_id":"5ab227cf07818240934b11a5",
        "player":"Peter",
        "comment":"",
        "points":1,
        "__v":0
      }
    ],
    "question":1,"__v":0
  }
]

I'm want to have a total score for each player based on this data, but I can't seem to find a code, to add up the points per player.

The result be something like: Peter: 14 André: 12 Maikel: 10 Iebele: 8

Any ideas on how to achieve this?

I've tried to get the points with the following code:

var { data, players } = this.state;
var ArrLength = data.length;
console.log(data);
var j;
var x;
for (j = 0; j < ArrLength; j++) {
  let answer = data[j].answers;
  for (x = 0; x < answer.length; x++) {
    console.log(answer[`${x}`].points);
  }
}

This at least show me the points per player in the console.log. But now adding them to get an end result is something I can't seem to figure out.

Nina Scholz · Accepted Answer · 2018-03-21 15:39:09Z

2

You could use a Map for counting and build an array with the data.

var data = [{ answers: [{ _id: "5ab227cf07818240934b11a5", player: "Peter", comment: "", points: 7, __v: 0 }, { _id: "5ab24bf3b8494c76fd0bb31a", player: "André", comment: "", points: 6, __v: 0 }, { _id: "5ab24bf7b8494c76fd0bb31b", player: "Maikel", comment: "", points: 5, __v: 0 }, { _id: "5ab24bfab8494c76fd0bb31c", player: "Iebele", comment: "", points: 4, __v: 0 }], player: "Pieter", question: 1, __v: 0, _id: "5ab24e5e49e0f20a06d73ab7" }, { answers: [{ _id: "5ab227cf07818240935b11a5", player: "Peter", comment: "", points: 7, __v: 0 }, { _id: "5ab24bf3b8494c76fd8bb31a", player: "André", comment: "", points: 6, __v: 0 }, { _id: "5ab24bf7b8494c76fd2bb31b", player: "Maikel", comment: "", points: 5, __v: 0 }, { _id: "5ab24bfab8494c76fd9bb31c", player: "Iebele", comment: "", points: 4, __v: 0 }], player: "Kareltje", question: 1, __v: 0, _id: "5ab24e5e49e0f20b86d73ab7" }],
    score = Array.from(
        data.reduce((m, { answers }) =>
            answers.reduce((n, { player, points }) =>
                n.set(player, (n.get(player) || 0) + points), m), new Map),
        ([player, score]) => ({ player, score })
    );

console.log(score);

.as-console-wrapper { max-height: 100% !important; top: 0; }

edited Mar 21, 2018 at 15:39

answered Mar 21, 2018 at 15:33

Nina Scholz

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2 Comments

BaconPancakes Over a year ago

I would always try to use a map function instead of different for-loops (for each, for in etc.), so this is imo the solution OP should choose to work with.

Maikey Over a year ago

I'm getting an data.reduce is not a function error when trying this code.

Ele · Accepted Answer · 2018-03-21 15:41:20Z

You can use this alternative.

Using the function reduce and the function forEach.

reduce to accumulate.
forEach to loop over the answers.

var data = [{    answers: [        {            _id: "5ab227cf07818240934b11a5",             player: "Peter",             comment: "",             points: 7,             __v: 0        }        , {            _id: "5ab24bf3b8494c76fd0bb31a",             player: "André",             comment: "",             points: 6,             __v: 0        }        , {            _id: "5ab24bf7b8494c76fd0bb31b",             player: "Maikel",             comment: "",             points: 5,             __v: 0        }        , {            _id: "5ab24bfab8494c76fd0bb31c",             player: "Iebele",             comment: "",             points: 4,             __v: 0        }    ],    player: "Pieter",    question: 1,    __v: 0,    _id: "5ab24e5e49e0f20a06d73ab7"},{    answers: [        {            _id: "5ab227cf07818240935b11a5",             player: "Peter",             comment: "",             points: 7,             __v: 0        },         {            _id: "5ab24bf3b8494c76fd8bb31a",             player: "André",             comment: "",             points: 6,             __v: 0        }        , {            _id: "5ab24bf7b8494c76fd2bb31b",             player: "Maikel",             comment: "",             points: 5,             __v: 0        }        ,{            _id: "5ab24bfab8494c76fd9bb31c",             player: "Iebele",             comment: "",             points: 4,             __v: 0        }    ],    player: "Kareltje",    question: 1,    __v: 0,    _id: "5ab24e5e49e0f20b86d73ab7"}];

var result = data.reduce((a, {answers}) => {
  answers.forEach(({player, points}) =>  a[player] = (a[player] || 0) + points);
  return a;
}, {});


console.log(result);

.as-console-wrapper { max-height: 100% !important; top: 0; }

I'm getting an data.reduce is not a function error when trying this code.

Chase DeAnda · Accepted Answer · 2018-03-21 15:38:48Z

1

You can use .reduce to iterate through the array and aggregate all the scores:

const data = [{"answers":[{"_id":"5ab227cf07818240934b11a5","player":"Peter","comment":"","points":7,"__v":0},{"_id":"5ab24bf3b8494c76fd0bb31a","player":"André","comment":"","points":6,"__v":0},{"_id":"5ab24bf7b8494c76fd0bb31b","player":"Maikel","comment":"","points":5,"__v":0},{"_id":"5ab24bfab8494c76fd0bb31c","player":"Iebele","comment":"","points":4,"__v":0}],"player":"Pieter","question":1,"__v":0,"_id":"5ab24e5e49e0f20a06d73ab7"},{"answers":[{"_id":"5ab227cf07818240935b11a5","player":"Peter","comment":"","points":7,"__v":0},{"_id":"5ab24bf3b8494c76fd8bb31a","player":"André","comment":"","points":6,"__v":0},{"_id":"5ab24bf7b8494c76fd2bb31b","player":"Maikel","comment":"","points":5,"__v":0},{"_id":"5ab24bfab8494c76fd9bb31c","player":"Iebele","comment":"","points":4,"__v":0}],"player":"Kareltje","question":1,"__v":0,"_id":"5ab24e5e49e0f20b86d73ab7"}];

const scores = data.reduce( (scores, d) => {
  
  d.answers.forEach( answer => {
    scores[answer.player] = (scores[answer.player]||0) + answer.points;
  });

  return scores;
}, {});

console.log(scores);

answered Mar 21, 2018 at 15:38

Chase DeAnda

16.5k3 gold badges34 silver badges41 bronze badges

4 Comments

Maikey Over a year ago

I'm getting an data.reduce is not a function error when trying this code.

Chase DeAnda Over a year ago

@Maikey I had to alter the example data you posted to be correct JSON. You can see the data I used in the example.

Maikey Over a year ago

I've editted the data in the post. That's the exact data I'm getting returned from mongodb. Still a data.reduce error. I've also checked it with the data you're using, but it seems the same to me...

Maikey Over a year ago

Never mind... already figured it out. Made a stupid mistake in the initial state. Had it set to {} instead of []. This was the reason why it didn't work.

Maurício Giordano · Accepted Answer · 2018-03-21 15:31:35Z

You can simply do it with an external array. It basically uses the same key for each element in points, it verifies if the key is set already (if not, sets as zero), and sums points related with same key.

PS: _id is not unique in your json.

Since the JSON you gave is not valid, I'm using the following one:

var arr = [
    {
        answers: [{
                _id: "5ab227cf07818240934b11a5", 
                player: "Peter", 
                comment: "", 
                points: 7, 
                __v: 0
            }, {
                _id: "5ab24bf3b8494c76fd0bb31a", 
                player: "André", 
                comment: "", 
                points: 6, 
                __v: 0
            }, {
                _id: "5ab24bf7b8494c76fd0bb31b", 
                player: "Maikel", 
                comment: "", 
                points: 5, 
                __v: 0
            }, {
                _id: "5ab24bfab8494c76fd0bb31c", 
                player: "Iebele", 
                comment: "", 
                points: 4, 
                __v: 0
            }
        ],
        player: "Pieter",
        question: 1,
        __v: 0,
        _id: "5ab24e5e49e0f20a06d73ab7"
    }, {
        answers: [{
                _id: "5ab227cf07818240935b11a5", 
                player: "Peter", 
                comment: "", 
                points: 7, 
                __v: 0
            }, {
                _id: "5ab24bf3b8494c76fd8bb31a", 
                player: "André", 
                comment: "", 
                points: 6, 
                __v: 0
            }, {
                _id: "5ab24bf7b8494c76fd2bb31b", 
                player: "Maikel", 
                comment: "", 
                points: 5, 
                __v: 0
            }, {
                _id: "5ab24bfab8494c76fd9bb31c", 
                player: "Iebele", 
                comment: "", 
                points: 4, 
                __v: 0
            }
        ],
        player: "Kareltje",
        question: 1,
        __v: 0,
        _id: "5ab24e5e49e0f20b86d73ab7"
    }
]

var points = {};
for (var i in arr) {
    for (var j in arr[i].answers) {
        if (!points[arr[i].answers[j].player]) {
            points[arr[i].answers[j].player] = 0;
        }
        points[arr[i].answers[j].player] += arr[i].answers[j].points;
    }
}

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