Javascript multiple value object to simple array

Question

I have an object like this:

obj1 = {A: {bottom: 63, mid: 4, top: 15}, B: {bottom: 30, mid: 23, top: 5}, C: {bottom: 41, mid: 25, top: 16}}

and I'm trying to convert to something like this:

obj2 = 
{group: "A", bottom: "63", mid: "4", top: "15"}
{group: "B", bottom: "30", mid: "23", top: "5"}
{group: "C", bottom: "41", mid: "25", top: "16"}

by following this post but I'm getting an error obj1[key].forEach is not a function any ideas why I'm getting this error?

this is the code I'm using which is basically the same from the original:

obj1 ={A: {bottom: 63, mid: 4, top: 15}, B: {bottom: 30, mid: 23, top: 5}, C: {bottom: 41, mid: 25, top: 16}}

const result = []

// for each key in obj
Object.keys(obj1).forEach(key => {
    // for each array element of the property obj[key]
    obj1[key].forEach((value, index) => {// in this line I'm getting the error
        // if an object doesn't exists at the current index in result
        // create it
        if (!result[index]) {
            result[index] = {}
        }
        // at the result index, set the key to the current value
        result[index][key] = value
    })
})
console.log(result)

obj1["A"] returns an object - not an array - you can use object.entries instead — Denis Tsoi
– Denis Tsoi, Commented May 5, 2020 at 15:41

brk · Accepted Answer · 2020-05-05 15:42:59Z

2

You are getting error because of this line obj1[key].forEach((value, index), because it is an object and you are trying to use forEach on an object.

For example obj1[key] will give the value of A and B etc keys which as an object like {bottom: 63, mid: 4, top: 15}.

You can us only for..in and then use destructing to push the values in the array

const obj1 = {
  A: {
    bottom: 63,
    mid: 4,
    top: 15
  },
  B: {
    bottom: 30,
    mid: 23,
    top: 5
  },
  C: {
    bottom: 41,
    mid: 25,
    top: 16
  }
}

const result = []

for (let key in obj1) {
  result.push(Object.assign({}, obj1[key], {
    group: key
  }))

}

console.log(result)

answered May 5, 2020 at 15:42

brk

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ray · Accepted Answer · 2020-05-05 15:47:49Z

1

forEach is available on arrays, but during the first iteration obj1[key] is effectively obj1.A, which returns an object {bottom: 63, mid: 4, top: 15}, which doesn't have forEach, hence the error.

This might be a good use of reduce:

obj1 = {A: {bottom: 63, mid: 4, top: 15}, B: {bottom: 30, mid: 23, top: 5}, C: {bottom: 41, mid: 25, top: 16}}

const result = Object.entries(obj1).reduce(
  // group is the key from obj1, e.g. "A"
  // properties is the object for that key, e.g. { bottom: 63, mid: 4, top: 15 }
  (acc, [group, properties]) => [
    ...acc, { group, ...properties }
  ], []
);

console.log(result);

edited May 5, 2020 at 15:47

answered May 5, 2020 at 15:41

ray

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Comments

Phin Jensen · Accepted Answer · 2020-05-05 15:47:06Z

0

obj1[key] will return an object like {bottom: 63, mid: 4, top: 15}, which doesnt have a forEach function. The simplest way to do what you are trying to do would be to add the group key to the object each loop and push it to results:

// for each key in obj
Object.keys(obj1).forEach(key => {
    obj1[key].group = key;
    result.push(obj1[key]);
})

answered May 5, 2020 at 15:47

Phin Jensen

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Comments

Ghanshyam Yadav · Accepted Answer · 2020-05-05 15:47:42Z

Currently, you are trying to iterate through an object obj1[key].forEach which does not have a forEach function. the function belongs to Array prototype.

Try this instead:

obj1 ={A: {bottom: 63, mid: 4, top: 15}, B: {bottom: 30, mid: 23, top: 5}, C: {bottom: 41, mid: 25, top: 16}}

const result = []

// for each key in obj
Object.keys(obj1).forEach(key => {
    // for each array element of the property obj[key]
    Object.keys(obj1[key]).forEach((value, index) => {// in this line I'm getting the error
        // if an object doesn't exists at the current index in result
        // create it
        if (!result[index]) {
            result[index] = {}
        }
        // at the result index, set the key to the current value
        result[index][key] = value
    })
})
console.log(result)

D. Seah · Accepted Answer · 2020-05-05 15:48:01Z

0

you can use a map function base on obj1's keys

    var obj1 = {A: {bottom: 63, mid: 4, top: 15}, B: {bottom: 30, mid: 23, top: 5}, C: {bottom: 41, mid: 25, top: 16}};

    var obj2 = Object.keys(obj1).map(function(k) {
      var clone = JSON.parse(JSON.stringify(obj1[k])); // use lobash for cloning
      clone.group = k;
      return clone;
    });

    console.log(obj2)

answered May 5, 2020 at 15:48

D. Seah

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joy08 · Accepted Answer · 2020-05-05 15:52:32Z

0

Iterating over the keys using Object.keys and followed by using .map to form the required result

var obj1 = {
  A: { bottom: 63, mid: 4, top: 15 },
  B: { bottom: 30, mid: 23, top: 5 },
  C: { bottom: 41, mid: 25, top: 16 }
};

var out = Object.keys(obj1).map(i => {
  return {
    group: i,
    ...obj1[i]
  };
});

console.log(out);

answered May 5, 2020 at 15:52

joy08

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