javascript lookup value of a map object which is array of array

Question

I have a JS map object (new to JS here) which is an array of array like so:

scores=[["key_1",true],["key_2",false],["key_3",false]....["key_n",true]]

I am able to access the values on the console like so:

scores[0] //outputs ["key_1",true]
scores[0][0] //outputs "key_"
//..and so on.

How do I however make a (fast) lookup for a particular key in the object array, something like:

scores[["key_3"]] //obviously wont work
//expected output: false

You also might want to consider using a Set() or an object with attributes if you're simply dealing with key/value pairs. — Trentium
– Trentium, Commented Dec 27, 2019 at 22:23
@JonTrent A Map, as in Patrick's comment, works with arrays of arrays and is as efficient as an object or Set. — Heretic Monkey
– Heretic Monkey, Commented Dec 27, 2019 at 22:27
@PatrickRoberts: please post this as an answer and I will accept this. This looks elegant. — John M
– John M, Commented Dec 27, 2019 at 22:28

Yousername · Accepted Answer · 2019-12-27 22:34:49Z

1

Use Object.fromEntries() to turn the array into an object.

Use Object.entries() to change back into array.

var scores = [
  ["key_1", true],
  ["key_2", false],
  ["key_3", false],
  ["key_4", true]
];

scores = Object.fromEntries(scores);

console.log(scores.key_3);

edited Dec 27, 2019 at 22:34

answered Dec 27, 2019 at 22:28

Yousername

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Comments

LukStorms · Accepted Answer · 2019-12-28 11:43:21Z

1

You can simply find the key.

const scores=[ ["key_1",true], ["key_2",false], ["key_3",false], ["key_4",true] ];

var score = scores.find(score => score[0]==="key_3")

console.log(score[0]+" is "+score[1])

Returns:

key_3 is false

You could also transform the array-of-arrays to a Map object.

To get an easy access to the key-value pairs, while it's still iterable.

const scores=[ ["key_1",true], ["key_2",false],["key_3",false], ["key_4",true] ]

var scoreMap = new Map();
scores.forEach(score => scoreMap.set(score[0], score[1]))
 
console.log("key_4 is "+ scoreMap.get("key_4"))
 
console.log([...scoreMap.keys()])

edited Dec 28, 2019 at 11:43

answered Dec 27, 2019 at 22:22

LukStorms

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3 Comments

John M Over a year ago

@LukStroms: For some reason, I like Patrick's answer.. Thoughts?

LukStorms Over a year ago

@JohnM If you do console.log(scores) after it, then you'll notice that his method turned the 2D array into an object. So if you use that trick, then I would probably use another variable name for it.

LukStorms Over a year ago

@JohnM I realised that since that array is basically containing key-value pairs, that using find for each key is indeed not optimal. So an alternative was added.

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