accessing values by key instead of index

Question

I read a json file (basically flat table) and dynamically nest the data. I get nested data similar to:

[{key: "AAA", value: 100}, {key: "BBB", value: 200}, {key: "CCC", value: 150}]

Accessing key and/or value by index is no problem, e.g. dat[0].key, dat[1].value. But how do I directly access a value by not using (because not knowing) its index. I.e. dat["BBB"].value or dat["AAA"].value

What is the usefulness of key/value pairs, if I still have to access the data via indexes. In my case this would mean, to first somehow determine the index of a specific key and then reference by key.

I am quite sure, this is a very stupid question and I apologize for it, but after several days of searching the net, I still was not able to find an answer.

Thanks an awful lot for any help

Using array find, `arr.find(x => x.key = 'AAA')` will return `{key: "AAA", value: 100}` (only the first instance) — evolutionxbox, Oct 11 '17 at 09:06
That doesnt work... You used `=` not `===` so `arr.find(x => x.key = 'BBB')` will just return the first item — notrota, Oct 11 '17 at 09:10
@gerardofutrado The dupe target only deals with objects, not an array of objects. — evolutionxbox, Oct 11 '17 at 09:13
@evolutionxbox here is another one. The fact is that we don't need this answered by the zillionth time, again. — Gerardo Furtado, Oct 11 '17 at 09:16
@GerardoFurtado fair enough. Thank you for updating the dupe target — evolutionxbox, Oct 11 '17 at 09:17
@gerardo furtado: Well, I see the relation, but did not find that five year old answer earlier. If so, I might have found my own solution without posting a question. Please do not feel urged to answer a question. If this has been questioned a "zillionth" time, then maybe because it is neither intuitively to solve nor properly documented. I needed an answer - and I honestly thank all who invested their time to help me. — PaLi, Oct 11 '17 at 13:31
@PaLi it's not your fault, you certainly can ask that question. My comment was addressed to the answerers that, instead of closing a question which is clearly a duplicate (by the way, this is very well documented), decided to answer it. — Gerardo Furtado, Oct 11 '17 at 23:11

anteAdamovic · Accepted Answer · 2017-10-11T09:15:14.493

1

A form of a map can be realized in JS via Objects.

Here's an example:

var data = {
  "key": "value"
}

console.log(data.key); // prints 'value'
console.log(data["key"]); // prints 'value'

You could parse the data into an object like:

function parseDataIntoObject(dataArray) {
  var data = {};
  dataArray.forEach(
    (object) => {
      data[object.key] = object.value;
    }
  );
  return data;
}

then you can fetch your data like data["AAA"].

I can provide more examples on the subject if needed.

edited Oct 11 '17 at 09:15

answered Oct 11 '17 at 09:07

anteAdamovic

1,462
12
23

Thanks very much! Well that's actually what I wanted, and I assumed I have an array of objects. I see the proposed solutions, but it just frustrates me more - what is the added value of key / value pairs if I cannot access a value by its associated key. – PaLi Oct 11 '17 at 13:25
Because a Map is not supported in JavaScript by default, you simply had an array of objects which doesn't qualify as a Map. If you find my answer helpful please mark it as correct. – anteAdamovic Oct 11 '17 at 13:27

evolutionxbox · Answer 2 · 2017-10-11T09:10:03.683

1

Using the Array find method:

let data = [{key: "AAA", value: 100}, {key: "BBB", value: 200}, {key: "CCC", value: 150}]

let item1 = data.find(x => x.key === 'AAA')
let item2 = data.find(x => x.key === 'BBB')
let item3 = data.find(x => x.key === 'CCC')

console.log(item1, item2, item3)

Please note: This will only return the first instance of an object with the matching key. For multiple objects, use one of the other solutions posted here.

edited Oct 11 '17 at 09:10

answered Oct 11 '17 at 09:08

evolutionxbox

3,932
6
34
51

This does not work, you used `=` so it will not work for `x.key = "BBB"` it will just return the first object – notrota Oct 11 '17 at 09:09
@GuyWhoKnowsStuff please may you review, and amend your comment and/or votes? – evolutionxbox Oct 11 '17 at 09:11

gurvinder372 · Answer 3 · 2017-10-11T09:07:26.350

0

Try something like

function getByKey( arr, key )
{
   var results = arr.filter( function( item ){ item.key == key });
   var value = results ? results[0].value : "" 
   return value; 
}

getByKey( data, "AAA" ); //this will return the value for AAA

edited Oct 11 '17 at 09:07

answered Oct 11 '17 at 09:05

gurvinder372

66,980
10
72
94

Well, quite an effort for a functionality that I intuitively had expected to be available. Obviously not, but I guess I will do exactly what you propose. "Outsourcing" the issue and use my own function. - Thanks! – PaLi Oct 11 '17 at 15:44

score 0 · Answer 4 · answered Oct 11 '17 at 09:06

This returns the first object matching with the key. You can change this according to your requirement if you want an array of multiple matching objects

 var data = [{key: "AAA", value: 100}, {key: "BBB", value: 200}, {key: "CCC", value: 150}];
 var keyToFilter = "AAA";//could be anything

 var resultObj = data.filter(function(obj){return obj.key === keyToFilter })[0];

score 0 · Answer 5 · answered Oct 11 '17 at 09:07

do

const arr = [{key: "AAA", value: 100}, {key: "BBB", value: 200}, {key: "CCC", value: 150}]

const item = arr.filter(obj => obj.key === "BBB")[0];

console.log(item.value);

Basically, this filters the array for the same key, then get the value by the first item

if there is no item, test for the following

if (item.length > 0) // ...

accessing values by key instead of index

5 Answers5