Group JavaScript Object by id

Question

I have a JavaScript object

I'm trying to group these objects by id, and produce a map of a list of names where the key is the id, and the value is the name. Example:

{1 : [John, Jane, Mike], 3: [Bob, Will]}

With the code below, I get:

{1: [John, Jane, Mike, Bob, Will], 3: [John, Jane, Mike, Bob, Will]}

How can I achieve my desired output? Any help would be appreciated.

var myObj = [{
    id: 1,
    name: "John",
    major: "accounting"
  },
  {
    id: 1,
    name: "Jane",
    major: "accounting"
  }, {
    id: 1,
    name: "Mike",
    major: "accounting"
  }, {
    id: 3,
    name: "Bob",
    major: "history"
  }, {
    id: 3,
    name: "Will",
    major: "history"
  }]



for (i in myObj) {
  var obj = myObj[i];
  var id = obj.id;
  var name = obj.name;
  var newMap = {};
  var namesArray = [];

  if (!(id in newMap)) {
    namesArray.push(name);
    newMap[id] = namesArray;

  } else {
    for (key in newMap) {
      if (key == id) {
        namesArray.push(name);
        newMap[key] = namesArray;
      }
    }
  }
  console.log(newMap);
}

I tried to create a snippet for you. The array was not a working solution and it does not need for (i in myObj) . Please fix the code and the object to reflect your comments — mplungjan
– mplungjan, Commented Feb 18, 2017 at 18:05

dev8080 · Accepted Answer · 2017-02-18 18:09:44Z

1

Editing your own program:

var myObj = [{
    id: 1,
    name: "John",
    major: "accounting"
  },
  {
    id: 1,
    name: "Jane",
    major: "accounting"
  }, {
    id: 1,
    name: "Mike",
    major: "accounting"
  }, {
    id: 3,
    name: "Bob",
    major: "history"
  }, {
    id: 3,
    name: "Will",
    major: "history"
  }]


  var newMap = {};
  var namesArray = [];
     
for (i in myObj) {
  var obj = myObj[i];
  var id = obj.id;
  var name = obj.name;

  if (!(id in newMap)) {
     namesArray = [];
     namesArray.push(name);
    newMap[id] = namesArray;

  } else {
        namesArray = newMap[id];
        namesArray.push(name);
     
  }
  
}
console.log(newMap);

answered Feb 18, 2017 at 18:09

dev8080

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1 Comment

Mihai Alexandru-Ionut Over a year ago

@developer-x, please have a look at my answer too.

Gerardo · Accepted Answer · 2017-02-18 18:14:24Z

0

var myObj = [{id: 1, name: "John", major:"accounting"},
            {id: 1, name: "Jane", major:"accounting"},
            {id: 1, name: "Mike", major:"accounting"},
            {id: 3, name: "Bob",  major:"history"},
            {id: 3, name: "Will", major:"history"}];

var group = {};

for(var i = 0; i < myObj.length; i++){
  if(myObj[i].id in group){
    group[myObj[i].id].push(myObj[i].name);
  } else {
    group[myObj[i].id] = [];
    group[myObj[i].id].push(myObj[i].name);
  }
}
console.log(group);

answered Feb 18, 2017 at 18:14

Gerardo

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Comments

Mohamed Abbas · Accepted Answer · 2017-02-18 18:25:52Z

0

Another solution using map function.

var objs = [{id: 1, name: "John", major:"accounting"},
            {id: 1, name: "Jane", major:"accounting"},
            {id: 1, name: "Mike", major:"accounting"},
            {id: 3, name: "Bob",  major:"history"},
            {id: 3, name: "Will", major:"history"}];

var namesForId = [], currentId = null, theObj = {};
objs.map((item) => {
    if (item.id === currentId) {
       namesForId.push(item.name);
    } else {
       currentId = item.id; 
       namesForId = [item.name];
       theObj[item.id] = namesForId;
    }    
})
console.log(theObj);

answered Feb 18, 2017 at 18:25

Mohamed Abbas

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Comments

score 0 · Accepted Answer · 2017-02-18 20:31:36Z

0

Another method that uses Array#reduce but a bit more compact.

const input = [{ id: 1, name: "John", major: "accounting" }, { id: 1, name: "Jane", major: "accounting" }, { id: 1, name: "Mike", major: "accounting" }, { id: 3, name: "Bob", major: "history" }, { id: 3, name: "Will", major: "history" } ];

console.log(input.reduce((m, e) => ((m[e.id] = m[e.id] || []).push(e.name), m), {}))

edited Feb 18, 2017 at 20:31

answered Feb 18, 2017 at 19:53

user4639281

Comments

frogatto · Accepted Answer · 2017-02-19 07:10:11Z

0

Using Array.prototype.reduce().

var myObj = [{id: 1, name: "John", major:"accounting"},
             {id: 1, name: "Jane", major:"accounting"},
             {id: 1, name: "Mike", major:"accounting"},
             {id: 3, name: "Bob",  major:"history"   },
             {id: 3, name: "Will", major:"history"   }];

var result = myObj.reduce(function(acc, item) {
  acc[item.id] = acc[item.id] || [];
  acc[item.id].push(item.name);
  return acc;
}, {});

console.log(result);

edited Feb 19, 2017 at 7:10

answered Feb 18, 2017 at 18:06

frogatto

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