Javascript - nested arrays transformed to array of objects

Question

I have a nested array data structure like this -

var arrays = [
        [
            ['firstName', 'Joe'], ['lastName', 'Blow'], ['age', 42], ['role', 'clerk']
        ],
        [
            ['firstName', 'Mary'], ['lastName', 'Jenkins'], ['age', 36], ['role', 'manager']
        ]
    ];

and I need to transform this into an array of objects -

[
        {firstName: 'Joe', lastName: 'Blow', age: 42, role: 'clerk'},
        {firstName: 'Mary', lastName: 'Jenkins', age: 36, role: 'manager'}
    ]..



    My code below gives- 

    function objectArray(arr) {
      var obj1 ={};
      var empData=[];
        for (var i = 0; i < arr.length; i++)
        {
            if (Array.isArray(arr[i]))
                { 
                  arr[i].reduce(function(acc,prd){
                   // console.log(prd);
                       console.log(acc.key=prd[0],acc.Value=prd[1]);//--> output shown below
                       return acc;
                  },{});
                }
        }
    }

     var returnArrayOfObjs = objectArray(arrays);
     var empData = [];
     empData.push(returnArrayOfObjs);
     console.log(empData);

The above log statement gives me an [undefined] as shown below in my output -

The output I get is as below - What am I doing wrong? Pls help!

firstName Joe
lastName Blow
age 42
role clerk
firstName Mary
lastName Jenkins
age 36
role manager
[undefined]

You are not storing the result of arr[i].reduce anywhere.

T4rk1n
– T4rk1n

2017-07-20 17:57:51 +00:00
Commented Jul 20, 2017 at 17:57 — T4rk1n
– T4rk1n, Commented Jul 20, 2017 at 17:57
@T4rk1n Thank you!

sunnysideup
– sunnysideup

2017-07-20 18:25:02 +00:00
Commented Jul 20, 2017 at 18:25 — sunnysideup
– sunnysideup, Commented Jul 20, 2017 at 18:25

sauntimo · Accepted Answer · 2017-07-20 18:02:04Z

2

I wrote a forEach() solution but map() / reduce() is probably more elegant so I upvoted @OriDrori :) Just posting this for comparison.

var arrays = [[['firstName', 'Joe'], ['lastName', 'Blow'], ['age', 42], ['role', 'clerk']],
        [['firstName', 'Mary'], ['lastName', 'Jenkins'], ['age', 36], ['role', 'manager']]
    ];

var rst = [];
    
 arrays.forEach(function(item){
    var obj = {};
    item.forEach(function( subitem, index ){
    	obj[ subitem[0] ] = subitem[1]
    });
    rst.push(obj);
 });
 
 console.log( rst );

answered Jul 20, 2017 at 18:02

sauntimo

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3 Comments

sunnysideup Over a year ago

Thanks @sauntimo.. I really do like forEach.. easier to read...was just trying to see why my reduce is failing.. thanks for your quick response!

sunnysideup Over a year ago

just a quick clarification.. in the above forEach are we not creating the obj every time.. meaning for every item...

sauntimo Over a year ago

Yeah, obj is var scoped to that function, think of it as a temporary store before we put the populated object in to the array

Ori Drori · Accepted Answer · 2017-07-20 18:04:26Z

2

Iterate the array with Array#map, and Array#reduce each sub array to an object.

const arr = [[["firstName","Joe"],["lastName","Blow"],["age",42],["role","clerk"]],[["firstName","Mary"],["lastName","Jenkins"],["age",36],["role","manager"]]];

const result = arr.map((subArr) => subArr.reduce((obj, [key, value]) => {
  obj[key] = value;
  return obj;
}, {}));

console.log(result);

edited Jul 20, 2017 at 18:04

answered Jul 20, 2017 at 17:59

Ori Drori

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4 Comments

sunnysideup Over a year ago

+1 for map and reduce...Thanks! I am using reduce too.. but don't know why the final object is not an object but just strings!

Ori Drori Over a year ago

@sunnysideup - In your code, inside the reduce you are not attaching the key and value correctly to the object, and you don't store the result of the reduce. So all the reduce does is console.log the strings you see.

sunnysideup Over a year ago

thank you v much! so obj.key and obj.Value does not really work.. we need to use bracket notation to attach the key values?

Ori Drori Over a year ago

Indeed. You have to assign the value to a key on the object obj[key] = value.

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