Get property with largest index key in object

Question

From the following object, how can I get the 'air' reading from the property with largest index key i.e. 4? (30.9)

{
  1: {
    air: "31.2",
    evap: "25.3",
    t_condenser: "43.8"
  },
  2: {
    air: "31.1",
    evap: "25.3",
    t_condenser: "43.6"
  },
  3: {
    air: "31.0",
    evap: "25.3",
    t_condenser: "43.5"
  },
  4: {
    air: "30.9",
    evap: "25.2",
    t_condenser: "43.3"
  }
}

I have tried the following, to try to get the last key, but it just reads undefined:

$.getJSON("handler.php?action=fetchLAE", function(data){

  console.log(data.length);

});

That's an object, not an array. Also it's not a "JSON array" either. JSON is a string format, not a data structure. — Derek 朕會功夫, Apr 14 '17 at 16:14
Why use an object for this? Why not use an array? Then instead of a scan, it's just `data[data.length-1].air`. — T.J. Crowder, Apr 14 '17 at 16:20

score 2 · Answer 1 · edited Dec 31 '19 at 19:59

Note: The data is badly formatted. That is what an array is for, your API returns an Object.

Solution: find the highest key in data (which is an Object):

data[Object.keys(data).sort().pop()].air

Explanation:

Object.keys(data)

Get all the properties as an array e.g. [1,4,3,2].

Now we sort it ascending and take the last:

.sort().pop()

So we take this property out of the object, and take its air value:

data[4].air

http://jsbin.com/setibevozu/edit?console

nitobuendia · Answer 2 · 2017-04-14T16:27:33.603

2

You can obtain the keys of the object with Object.keys() and then use Math.max to get the highest one.

var json = {
  1: {
    air: "31.2",
    evap: "25.3",
    t_condenser: "43.8"
  },
  2: {
    air: "31.1",
    evap: "25.3",
    t_condenser: "43.6"
  },
  3: {
    air: "31.0",
    evap: "25.3",
    t_condenser: "43.5"
  },
  4: {
    air: "30.9",
    evap: "25.2",
    t_condenser: "43.3"
  }
};


var maxKey = Math.max(...Object.keys(json));
var lastElementAir = json[maxKey].air;

console.log(lastElementAir);

edited Apr 14 '17 at 16:27

answered Apr 14 '17 at 16:22

nitobuendia

1,228
7
18

2

Just a side note, this answer uses the spread operator which is only available in ES6+. Equivalent in ES5: `Math.max.apply(Math, +Object.keys(json))`. – Derek 朕會功夫 Apr 14 '17 at 16:25

score 1 · Answer 3 · answered Apr 14 '17 at 16:19

1

This is not a valid JSON, but a javascript object.

You can make use of the Object.keys function to get the object properties and then get to the last element or property using the length property.

console.log(obj[Object.keys(obj).length].air);

var obj = {
1: {
air: "31.2",
evap: "25.3",
t_condenser: "43.8"
},
2: {
air: "31.1",
evap: "25.3",
t_condenser: "43.6"
},
3: {
air: "31.0",
evap: "25.3",
t_condenser: "43.5"
},
4: {
air: "30.9",
evap: "25.2",
t_condenser: "43.3"
}
};

console.log(obj[Object.keys(obj).length].air);

answered Apr 14 '17 at 16:19

Abhinav Galodha

9,293
2
31
41

This assumes that the object only contains continuous numeric keys and starts at 1. – Derek 朕會功夫 Apr 14 '17 at 16:22
@Derek朕會功夫, yes that's what the data contains in the OP. – Abhinav Galodha Apr 14 '17 at 16:25

Get property with largest index key in object

3 Answers3