How to loop over nested objects and arrays Javascript?

Question

I have an object which consists of keys and values as lists

myObj = { "key1": [{"value": 1, "date": "2020"}], [{"value": 2, "date": "2020"}],
          "key2": [{"value": 3, "date": "2020"}], [{"value": 4, "date": "2020"}]
        }

I need to get the value of "value" key in this nested objects and reassign it as an array to the key.

So my ideal result is

myObj = { "key1": [1,2],
          "key2": [3,4]
        }

What I did

So I tried to loop over the object

for (var [k, v] of Object.entries(myObj)) {
        v.forEach(function convertJSON(arr) {
            console.log(arr.value);
        });
        console.log(k, v);
    }

It works,

1
2
"key1": [{"value": 1, "date": "2020"}], [{"value": 2, "date": "2020"}]
3
4
"key2": [{"value": 3, "date": "2020"}], [{"value": 4, "date": "2020"}]

but when I tried to reassign the value it gives me undefined

for (var [k, v] of Object.entries(myObj)) {
        newValue = v.forEach(function convertJSON(arr) {
            console.log(arr.value);
        });
        v = newValue;
        console.log(k, v);
    }

UPDATE - Add my data

so I think it should like this

myData = { "impressions": [{value: 559, end_time: "2020-08-31T07:00:00+0000"}], 
                          [{value: 519, end_time: "2020-09-01T07:00:00+0000"}],
           "reach":      [{value: 334, end_time: "2020-08-31T07:00:00+0000"}],
                         [{value: 398, end_time: "2020-09-01T07:00:00+0000"}}

}

Nina Scholz · Accepted Answer · 2020-11-05 13:07:49Z

1

You could take a flat map of the nested objects.

const
    object = { key1: [{ value: 1, date: "2020" }, { value: 2, date: "2020" }], key2: [{ value: 3, date: "2020" }, { value: 4, date: "2020" }] },
     result = Object.fromEntries(Object
         .entries(object)
         .map(([k, v]) => [k, v.map(({ value }) => value)])
     );
     
console.log(result);

edited Nov 5, 2020 at 13:07

answered Nov 5, 2020 at 12:37

Nina Scholz

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1 Comment

Anna Over a year ago

Cool, but unfortunately for me it returns Uncaught TypeError: a.map is not a funct

phi-rakib · Accepted Answer · 2020-11-06 07:15:49Z

You can use Array.prototype.reduce() method to achieve your desired output. The syntax of array reduce array.reduce(function(total, currentValue, currentIndex, arr), initialValue). First get all the keys using Object.keys() method and then traverse it and map each item of that keyed object by using Array.prototype.map() method.

const myObj = {
  impressions: [
    { value: 559, end_time: '2020-08-31T07:00:00+0000' },
    { value: 519, end_time: '2020-09-01T07:00:00+0000' },
  ],
  reach: [
    { value: 334, end_time: '2020-08-31T07:00:00+0000' },
    { value: 398, end_time: '2020-09-01T07:00:00+0000' },
  ],
};

const ret = Object.keys(myObj).reduce((prev, c) => {
  const p = prev;
  p[c] = myObj[c].map((x) => x.value);
  return p;
}, {});
console.log(ret);

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