How to get a key of a value from a java script Object? [duplicate]

Question

Following is an example of js object:

var arr =          
{
      "a1": { "0.25": 13, "0.5": 50},
      "a2": { "0.5": 50, "0.75": 113, "1": 202}
}

id = 'a1';
key = "0.25";

function myFunc(id, key) {
  return arr[id][key];
}

Using the above function I can get the value of the corresponding key.

My question how can I get the Key for a given value?

E.g. if id = 'a2' and value = 113, the function should return the corresponding key 0.75

Have a look at this answer to the same question: stackoverflow.com/questions/9907419/… — flppv
– flppv, Commented Mar 16, 2019 at 3:26
It’s important to note that this is not a multidimensional array. There are no arrays in your code. This is an object where each key is a string and the values are objects. An array would be [1,2,3]. — Nate
– Nate, Commented Mar 16, 2019 at 3:27
I agree it's not an array but its an Object. thanks for correcting and thank you all for the help. — ravi
– ravi, Commented Mar 16, 2019 at 3:34

ellipsis · Accepted Answer · 2019-03-16 03:31:18Z

1

You can use Object.entries to get the key

var arr = {
  "a1": {
    "0.25": 13,
    "0.5": 50
  },
  "a2": {
    "0.5": 50,
    "0.75": 113,
    "1": 202
  }
}

function myFunc(a, key) {
  var k = Object.entries(arr[a]).flat();
  return k[k.indexOf(key) - 1]
}
console.log(myFunc('a1', 13))

answered Mar 16, 2019 at 3:31

ellipsis

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Comments

Code Maniac · Accepted Answer · 2019-03-16 03:35:17Z

1

You can get keys for arr[a] first and than filter key based on value

var arr ={"a1": { "0.25": 13, "0.5": 50},"a2": { "0.5": 50, "0.75": 113, "1": 202}}

let a = 'a1',val = 13;

let getKey = (a,val) =>  Object.keys(arr[a]).filter(e => arr[a][e] === val)

console.log(getKey(a,val))
console.log(getKey('a2',113))

If you're sure that there's always one key with matching value or you want the first matching values key only than you can use find instead of filter

var arr ={"a1": { "0.25": 13, "0.5": 50},"a2": { "0.5": 50, "0.75": 113, "1": 202}}

let a = 'a1',val = 13;

let getKey = (a,val) =>  Object.keys(arr[a]).find(e => arr[a][e] === val)

console.log(getKey(a,val))
console.log(getKey('a2',113))

edited Mar 16, 2019 at 3:35

answered Mar 16, 2019 at 3:26

Code Maniac

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4 Comments

Bhojendra Rauniyar Over a year ago

How is that an array?

Code Maniac Over a year ago

@BhojendraRauniyar because i using filter in case there are more than one key which are having value than i am taking all the keys

Bhojendra Rauniyar Over a year ago

I meant to the object to which OP is calling an array. You should state that's not an array in your answer.

Code Maniac Over a year ago

@BhojendraRauniyar oops i thought were asking about the output of first snippet is in array :P OP already updated his question with proper naming

prasanth · Accepted Answer · 2019-04-18 04:55:13Z

0

Use Object.entries() and Array#find

var arr ={"a1": { "0.25": 13, "0.5": 50},"a2": { "0.5": 50, "0.75": 113, "1": 202}}

var a = 'a2',val = 113;

var Key = (a,val) =>  Object.entries(arr[a]).find(i=> i[1] == val)[0];

console.log(Key(a,val))

edited Apr 18, 2019 at 4:55

answered Mar 16, 2019 at 3:35

prasanth

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2 Comments

Code Maniac Over a year ago

On Side note:- It's worth mentioning that find will give only the first matching value's key. if there are more than one matching value's it won't return all the keys

prasanth Over a year ago

@CodeManiac .Op not mention multiple matching

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