How to Return a next value from an array of array

Question

I need to iterate the next value from an array of an array in every function call.

forex: If I have an array of array

const Arr = [ ['1','2', '3'], ['11','12', '13'], ['11','22', '33'],]

and I have a function

getNumber(id: number): string {
 let n;
 for(const i in Arr) {
    for(const j in Arr[i]{
       n = j;
    }
 }
 return n;
}

and I here I need to call the function multiple times but every Time It should return the next number

let i = 4;
for(let j=0; j<=i; j++) {
  const g = { 
   number: this.getNumber(i); //this i means id
  }
}

after the calling function, it will return like

'1'
'2'
'3'
'11'
'12'

please help me to solve this

StackByMe · Accepted Answer · 2020-11-24 12:02:03Z

6

You can use a generator to get the next value everytime you call the function.

To turn the multidimensional array into a flat array you can use the Array.flat() method.

const Arr = [ ['1','2', '3'], ['11','12', '13'], ['11','22', '33'],];

function* getNumber(arr) {  
  for(const num of arr) {
    yield num;
  }
}

const gen = getNumber(Arr.flat());

console.log(gen.next().value);
console.log(gen.next().value);
console.log(gen.next().value);
console.log(gen.next().value);
console.log(gen.next().value);

answered Nov 24, 2020 at 12:02

StackByMe

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3 Comments

Shubham Patil Over a year ago

I need to assign that value to id

Barremian Over a year ago

@ShubhamPatil: let id = gen.next().value?

StackByMe Over a year ago

@ShubhamPatil I'm not sure what you mean, you don't seem to use the id in your code snippet. If you need to assign the return value to a variable called id you can just do the following: const id = gen.next().value

user1 · Accepted Answer · 2020-11-25 08:43:08Z

You can use the build-in Array Iterator that uses a generator like the one shown in the answer from @Reyno. It's just simpler and you don't have to write so much code since it's already written for you.

const arr = [[1],[2],[3],[4]];
const it = arr.flat()[Symbol.iterator]();
it.next() // { value: 1, done: false }
it.next() // { value: 2, done: false }
it.next() // { value: 3, done: false }
it.next() // { value: 4, done: false }
it.next() // { value: undefined, done: true }

Also if you don't want to use generators and iterators since they are from ES6, you can just write a function:

function getIterator(arr) {
  var counter = 0;
  return function next() {
    if (counter === arr.length) { return undefined; }
    return arr[counter++]; 
  };
}

var arr = [1, 2, 3, 4];
var next = getIterator(arr);
next(); // 1
next(); // 2
next(); // 3
next(); // 4
next(); // undefined
next(); // undefined
arr.push(5);
next(); // 5

which by the way can be even a better solution even in ES6+ since you will be able to push elements inside the array and still be able to iterate over the new ones. The iterator/generator solution closes after reaching the end of the array so you must create a new one in order to iterate over again.

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