get array from the object using map in javascript. but getting array with undefined

Question

I am using map to get the sub part of the array.

var mappingobj = {"custom":[{"head":"202","sub":["302","303"]},{"head":"203","sub":["102"]}],"spec":[]};

var subids = mappingobj.custom.map(function(o, i) {
      if(o.head==202){
       return o.sub;
      }
});

console.log(subids);

I need to get only ["302","303"]. but i am getting the output as [Array[2], undefined].

The undefined comes because only when your "non-strict equality" head matches 202 you return the sub, the other onces do not, so they return undefined — Icepickle
– Icepickle, Commented Nov 27, 2017 at 10:20

HimanshuArora9419 · Accepted Answer · 2017-11-27 10:33:40Z

3

Basic Idea is that map is to get certain value out of array. if you don't return anything in map by default undefined will be return and you will get undefined.So use filter to get desired object and than use map to get desired property of that object

var mappingobj = {"custom":[{"head":"202","sub":["302","303"]},{"head":"203","sub":["102"]}],"spec":[]};

var subids = mappingobj.custom.filter(function(o, i) {
      if(o.head==202 && o.head){
       return o;
      }
}).reduce((acc,elem)=>{acc.push(...elem.sub); return acc;},[]);

console.log(subids);

edited Nov 27, 2017 at 10:33

answered Nov 27, 2017 at 10:22

HimanshuArora9419

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2 Comments

ramu Over a year ago

yes exactly correct. but i want the single dimensional array can u help me like [302,303]

HimanshuArora9419 Over a year ago

check updated code. Even if there are multiple head with given value it will merge all of them in one arrat

Rayon · Accepted Answer · 2017-11-27 10:27:27Z

0

Hi you can try this.

var mappingobj = {
  "custom": [{
    "head": "202",
    "sub": ["302", "303"]
  }, {
    "head": "203",
    "sub": ["102"]
  }],
  "spec": []
};

var subids = mappingobj.custom.filter(function(o, i) {
  if (o.head == 202) {
    return o.sub;
  }
});

console.log(subids);

Hope this help you.

edited Nov 27, 2017 at 10:27

Rayon

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answered Nov 27, 2017 at 10:22

Sultan Khan

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2 Comments

Sultan Khan Over a year ago

it will work dude, as you are already returning an array, try it out.

Rayon Over a year ago

It will return array of objects, OP is expecting one dimensional array....

Niklesh Raut · Accepted Answer · 2017-11-27 10:32:34Z

0

You can find indexOf of head first and then get sub of mapping.custom

var mappingobj = {"custom":[{"head":"202","sub":["302","303"]},{"head":"203","sub":["102"]}],"spec":[]};
var obj = mappingobj.custom;
var index = obj.map(function (e) { return e.head; }).indexOf("202");
console.log(obj[index].sub);

answered Nov 27, 2017 at 10:32

Niklesh Raut

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