Looping through array and assigning new array's key

Question

I am trying to create a new array with it's key being the index of the old array

var array = [
          {"tom": "red", "part":"green", "brow_id":45},
          {"tom": "red", "part":"yellow", "brow_id":1},
          {"tom": "red", "part":"yellow", "brow_id":2},
          {"tom": "maroon", "part":"cyan", "brow_id":45}
           ];
var newarray = {};

array.forEach(function(elem) {
        newarray[elem.brow_id] = elem;
                    });

The newly formed array is like this

         45: {"tom": "red", "part":"green", "brow_id":45},
         1:  {"tom": "red", "part":"yellow", "brow_id":1},
         2:  {"tom": "red", "part":"yellow", "brow_id":2},

I want it to contain all the id's of the old array like this

        45: [{"tom": "red", "part":"green", "brow_id":45},{"tom": "maroon", "part":"yellow", "brow_id":45}]
         1:  {"tom": "red", "part":"yellow", "brow_id":1},
         2:  {"tom": "red", "part":"yellow", "brow_id":2},

What's wrong?

later you have a mixed reuslt of single objects and arrays with objects. — Nina Scholz
– Nina Scholz, Commented Mar 29, 2018 at 19:28
if u notice , newly formed array u saying is just an object . — Sachin
– Sachin, Commented Mar 29, 2018 at 19:31
@NinaScholz I just want a multi-dimensional array in index 45, doesn't matter if it's an object or array . Is there any chance to work by assigning as my code does — John Doe
– John Doe, Commented Mar 29, 2018 at 19:37
Curiosity, why was accepted other answer and not mine? Just to know. — Ele
– Ele, Commented Mar 29, 2018 at 19:56
@Ele because array.reduce doesn't work in my code. Nina's code worked — John Doe
– John Doe, Commented Mar 29, 2018 at 20:21

Nina Scholz · Accepted Answer · 2018-03-29 19:48:48Z

1

You could check if the property is given and assign the element, otherwise check for array and if not create an array. Later push the element.

var array = [{ tom: "red", part: "green", brow_id: 45 }, { tom: "red", part: "yellow", brow_id: 1 }, { tom: "red", part: "yellow", brow_id: 2 }, { tom: "maroon", part: "cyan", brow_id: 45 }],
    object = {};

array.forEach(function(elem) {
      if (!object[elem.brow_id]) {
          object[elem.brow_id] = elem;
          return;
      }
      if (!Array.isArray(object[elem.brow_id])) {
          object[elem.brow_id] = [object[elem.brow_id]];
      }
      object[elem.brow_id].push(elem);
});

console.log(object);

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edited Mar 29, 2018 at 19:48

answered Mar 29, 2018 at 19:45

Nina Scholz

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Comments

Ele · Accepted Answer · 2018-03-29 20:03:29Z

1

You can use the function reduce to group and build the desired output.

var array = [{    "tom": "red",    "part": "green",    "brow_id": 45  },  {    "tom": "red",    "part": "yellow",    "brow_id": 1  },  {    "tom": "red",    "part": "yellow",    "brow_id": 2  },  {    "tom": "maroon",    "part": "cyan",    "brow_id": 45  }];

var result = array.reduce((a, elem) => {
  if (a[elem.brow_id]) {
    if (Array.isArray(a[elem.brow_id])) a[elem.brow_id].push(elem);
    else a[elem.brow_id] = [elem, a[elem.brow_id]];
  } else a[elem.brow_id] = elem; 
  
  return a;
}, {});

console.log(result);

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Using your approach with forEach with a fix to check already added elements to the new object.

var array = [{    "tom": "red",    "part": "green",    "brow_id": 45  },  {    "tom": "red",    "part": "yellow",    "brow_id": 1  },  {    "tom": "red",    "part": "yellow",    "brow_id": 2  },  {    "tom": "maroon",    "part": "cyan",    "brow_id": 45  }];

var newarray = {};

array.forEach(function(elem) {
  if (newarray[elem.brow_id]) {
    if (Array.isArray(newarray[elem.brow_id])) newarray[elem.brow_id].push(elem);
    else newarray[elem.brow_id] = [elem, newarray[elem.brow_id]];
  } else newarray[elem.brow_id] = elem;  
});

console.log(newarray);

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edited Mar 29, 2018 at 20:03

answered Mar 29, 2018 at 19:27

Ele

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2 Comments

John Doe Over a year ago

The updated code works, but is it possible to check if the newarray has only arrays inside it, and if there are single elements like "tom": "red", "part": "yellow", "brow_id": 1 assign it to have an array and 0th element will have "tom": "red", "part": "yellow", "brow_id": 1

Ele Over a year ago

@JohnDoe can you post that requirement within the question's body?

Ori Drori · Accepted Answer · 2018-03-29 20:10:16Z

0

Grouping using Array.forEach():

var array = [{"tom":"red","part":"green","brow_id":45},{"tom":"red","part":"yellow","brow_id":1},{"tom":"red","part":"yellow","brow_id":2},{"tom":"maroon","part":"cyan","brow_id":45}];

var result = {};

array.forEach(function(o) {
  var key = o['brow_id'];
  
  result[key] = key in result ? [].concat(result[key], o) : o;
});

console.log(result);

edited Mar 29, 2018 at 20:10

answered Mar 29, 2018 at 19:29

Ori Drori

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