Javascript: How do I get the index of a certain order of values in an array?

Question

I'm currently trying to create a markov chain. Right now, I need to get the index of some values in an array. Is there any way that is possible?

I tried to use indexOf, but that only supports one argument.

Let's assume there is a function named INDEX that does what I need.

const arr = [1, 2, 3, 4, 3, 2, 3, 1];
INDEX(arr, [1, 2]) // returns 0, because 1, 2 is in the first index in the array.
INDEX(arr, [3, 4, 3]) // returns 2, because 3, 4, 3 starts at the third index.
INDEX(arr, [2, 3]) // returns 1, because there are two 2, 3s, so it returns the first.
INDEX(arr, [5, 6]) // returns -1, because it is not in the array.
INDEX(arr, [1, 4]) // even though these values are in the array, they aren't in the order, so returns -1

how large can your array be?

Pavan Skipo
– Pavan Skipo

2019-10-09 04:54:55 +00:00
Commented Oct 9, 2019 at 4:54 — Pavan Skipo
– Pavan Skipo, Commented Oct 9, 2019 at 4:54
Could you treat it like a string and use substr?

dwjohnston
– dwjohnston

2019-10-09 04:55:02 +00:00
Commented Oct 9, 2019 at 4:55 — dwjohnston
– dwjohnston, Commented Oct 9, 2019 at 4:55
@pavanskipo Around 2 - 12 in length.

William Will
– William Will

2019-10-09 04:57:44 +00:00
Commented Oct 9, 2019 at 4:57 — William Will
– William Will, Commented Oct 9, 2019 at 4:57

CertainPerformance · Accepted Answer · 2019-10-09 04:54:48Z

5

Use .findIndex, and check whether every one of the array items follows the current index:

const arr = [1, 2, 3, 4, 3, 2, 3, 1];

const INDEX = (arr, toFind) => arr.findIndex(
  (_, baseI, arr) => toFind.every((item, i) => arr[baseI + i] === item)
);

console.log(
  INDEX(arr, [1, 2]), // returns 0, because 1, 2 is in the first index in the array.
  INDEX(arr, [3, 4, 3]), // returns 2, because 3, 4, 3 starts at the third index.
  INDEX(arr, [2, 3]), // returns 1, because there are two 2, 3s, so it returns the first.
  INDEX(arr, [5, 6]), // returns -1, because it is not in the array.
  INDEX(arr, [1, 4]) // even though these values are in the array, they aren't in the order, so returns -1
);

answered Oct 9, 2019 at 4:54

CertainPerformance

373k55 gold badges354 silver badges359 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

William Will Over a year ago

Thank you! This was what I needed! My life purpose is fulfilled now.

Paaarth Over a year ago

@WilliamWill Please accept the answer.. if it works for you

Ashish · Accepted Answer · 2019-10-09 06:14:16Z

1

A very simple and neat approach is to deal with strings in this case.

So you can convert both the arrays to strings and use String.prototype.indexOf()

const INDEX = (arr, toFind) => arr.join('').indexOf(toFind.join(''))

const arr = [1, 2, 3, 4, 3, 2, 3, 1]

const INDEX = (arr, toFind) => arr.join('').indexOf(toFind.join(''))

console.log(
  INDEX(arr, [1, 2]),
  INDEX(arr, [3, 4, 3]),
  INDEX(arr, [2, 3]),
  INDEX(arr, [5, 6]),
  INDEX(arr, [1, 4])
)

edited Oct 9, 2019 at 6:14

answered Oct 9, 2019 at 6:09

Ashish

4,3801 gold badge19 silver badges46 bronze badges

1 Comment

CertainPerformance Over a year ago

This will not be reliable if the array items are outside the single digits, or if they're decimal, or if they're non-numbers

Collectives™ on Stack Overflow

Javascript: How do I get the index of a certain order of values in an array?

2 Answers 2

2 Comments

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

2 Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related