Get the first value from a nested object

Question

I have an object called allInvalidFields which lists invalid fields under an identifier e.g _0 or _3

The object could look like this

allInvalidFields = {
    "_0" : {
        0: input.foo,
        1: select.la
    }
    "_1" : {
        0: input.foofoo,
        1: select.lala
    }
}

But equally it could not have _0 as the first key and could look like this:

allInvalidFields = {
    "_1" : {
        0: input.alice,
        1: select.bob
    }
    "_3" : {
        0: input.foo
    }
}

How can I get the first value from the first object in the list? So in the example above it would be input.foo or input.alice depending on which dataset was being searched.

The notion "first" explicitly does not make sense with JavaScript objects. Properties are in no particular order. If you need predictable order, use an array. — Pointy, Feb 08 '17 at 15:45
@Pointy I am so stuck, because if I add to an array then I cannot use key and value pairs which I need e.g `_1` but if I add to an object then there is no first as you say. I'm totally lost. I have been trying to find a solution fr 5 days now. — user1486133, Feb 08 '17 at 15:49
This is not possible. Keys/properties/fields in a JavaScript Objects does not have any order. You cannot sort a javascript object as with an array.http://stackoverflow.com/a/5525820/3359432 — Nidhin David, Feb 08 '17 at 15:50
Well you can impose your own ordering on the property names by keeping them in an adjunct array in whatever order makes sense for your purposes. — Pointy, Feb 08 '17 at 15:50

programaths · Answer 1 · 2017-02-08T16:01:08.290

1

Inferred that the keys are in numeric order and prepended with "_".

Under these assumptions :

function first(obj,n){
  let smallest = Infinity;
  for(i in obj){
    console.log(i);
    let val='';
    if (i.toString()[0]=='_'){
      val = parseInt(i.toString().substring(1));
    }else{
      val = i;
    }
    if( val < smallest ){
      smallest = val;
    }
  }
  if(n>0){
     return first(obj["_"+smallest],n-1);
  }
  return obj[smallest];
}

first({"_0" : {
    0: "input.foo",
    1: "select.la"
},
"_1" : {
    0: "input.foofoo",
    1: "select.lala"
}},1); // input.foo

edited Feb 08 '17 at 16:01

answered Feb 08 '17 at 15:53

programaths

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obj["_"+Object.keys(obj).map(el=>el=+el.replace("_")).sort()[0]][0]... a bit shorter – Jonas Wilms Feb 08 '17 at 16:12
A bit more cryptic :-D Also, with mine, you can chose depth ! – programaths Feb 08 '17 at 16:27

score -1 · Answer 2 · answered Feb 08 '17 at 15:52

-1

You need something like this.

var allInvalidFields = {
  "_0": {
    "0": "input.foo",
    "1": "select.la"
  },
  "_1": {
    "0": "input.foofoo",
    "1": "select.lala"
  }
};

var firstInput = Object.keys(allInvalidFields)[0];
console.log(allInvalidFields[firstInput][0]);

answered Feb 08 '17 at 15:52

VHS

8,698
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Please read this answer and correct your answer http://stackoverflow.com/a/5525820/3359432 – Nidhin David Feb 08 '17 at 15:54
@NidhinDavid. here the OP is simply concerned about getting the first element - whatever it is - from the subarray - not necessarily the first one that was added to the subarray. – VHS Feb 08 '17 at 16:20
What I meant is that there is no such thing as 'first' or 'last' key in Javascript object. Thats what the link says. – Nidhin David Feb 08 '17 at 16:25
I agree. But here the OP is asking for a random first element. – VHS Feb 08 '17 at 16:26
The OP has made text bold. – Nidhin David Feb 08 '17 at 16:27

Jonas Wilms · Answer 3 · 2017-02-08T16:14:34.087

-1

Object.values(allInvalidFields)[0][0];

take the first value of the first property object.

Small note: having such keys like _1 is bad style...

Short version of programaths answer:

allInvalidFields["_"+Object.keys(allInvalidFields).map(el=>el=+el.replace("_","")).sort()[0]][0]

edited Feb 08 '17 at 16:14

answered Feb 08 '17 at 15:56

Jonas Wilms

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The problem is that there's no guarantee what that ordering will be. There'll definitely be a first value, but it may or may not be what the OP considers "first". – Pointy Feb 08 '17 at 15:57
If you pull first field, then it may not always the same as js objects does not implement order for its keys/fields http://www.stackoverflow.com/a/5525820/3359432 – Nidhin David Feb 08 '17 at 15:58
Missing depth flexibility of my answer ;-) – programaths Feb 08 '17 at 16:28

Get the first value from a nested object

3 Answers3