CODEWITHSUNDEEP
javascriptarrays
Tadas V.
Tadas V.

Reputation: 835

Find next array index not from start AND if not found loop from beginning

const arr = [{item:'a', value:false}, {item:'b', value:true}, {item:'c', value:true}, {item:'d', value:false}];
const startIndex = 2;

Given startIndex find next object in array with value=true. Iteration must be forward and, if not found, start from index 0. Should return arr[1];

I've just hit the wall and seems can't find an iteration method:/

let result = {};
for (let i = startIndex + 1; i < arr.length; i++) {
    if (!arr[i] && i < arr.length) {
        result = arr[i];
    }
}
console.log(result);

Upvotes: 1

Views: 1738

Answers (3)

Majed Badawi
Majed Badawi

Reputation: 28414

You can use .splice to create the two halves:

  • First, search for the element with value=true in the second half, if found, keep in mind to add the length of the first to the index
  • If not found in the second part, search in the first one

const getElementAtIndexFromStart = (arr=[], startIndex=0) => {
  // get index of element if exists starting from startIndex
  let index = arr.slice(startIndex+1).findIndex(({value}) => value===true);
  if(index!==-1) {
    // if found, add the start index to it to represent the position in in arr
    index = index + startIndex + 1;
  } else {
    // if not found in the second half, search in the first one
    index = arr.slice(0, startIndex+1).findIndex(({value}) => value===true);
  }
  return arr[index];
}

const arr = [{item:'a', value:false}, {item:'b', value:true}, {item:'c', value:true}, {item:'d', value:false}];

console.log('Start: 0 => ', getElementAtIndexFromStart(arr, 0));
console.log('Start: 1 => ', getElementAtIndexFromStart(arr, 1));
console.log('Start: 2 => ', getElementAtIndexFromStart(arr, 2));
console.log('Start: 3 => ', getElementAtIndexFromStart(arr, 3));
console.log('Start: 5 => ', getElementAtIndexFromStart(arr, 5));

Upvotes: 1

Samir Ribeiro
Samir Ribeiro

Reputation: 205

I'm not sure if I understood. But...

getNext = function(startIndex, arr){
    var i;
    for(i = startIndex; i < arr.length; i++){
        if(arr[i].value){
            return arr[i];
        }
    }

    if(startIndex != 0){
        return getNext(0, arr);
    }
    return null;
}

Upvotes: 1

Nina Scholz
Nina Scholz

Reputation: 386550

You could take a single loop and take startIndex as offset and shape the index by the remainder with the length.

const
    array = [{ item: 'a', value: false }, { item: 'b', value: true }, { item: 'c', value: true }, { item: 'd', value: false }],
    startIndex = 3;
    
let result;

for (let i = startIndex; i < array.length + startIndex; i++) {
    console.log(i, i % array.length);
    if (array[i % array.length].value) {
        result = array[i % array.length];
        break;
    }
}

console.log(result);

Upvotes: 1

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