In the below code:

1. First I create an array of 10 elements
2. Next I remove 3 random elements from that array.
3. I try to add those 3 random elements into the original array in the original positions.

For some reason in step 3 above (in the FINAL ARR console log), the elements are being added in the wrong position. Is my slice function incorrect in step 3? If so, how do I modify it to be correct?

// Step 1. Create array of 10 elements
const originalValues = maxAmount => {
  let finalArray = [];
  for (let i = 0; i < maxAmount; i  ) {
    finalArray.push({
      key1: `key1-${i 1}`,
      position: i
    });
  }
  return finalArray;
}
let finalArr = originalValues(10);
const finalArrOriginalLength = finalArr.length;

//Step 2. Remove 3 random elements in this case key1-2, key1-7, key1-8
const removedElements = [];
finalArr = finalArr.filter(elem => {
  if (elem.key1 === 'key1-7' || elem.key1 === 'key1-2' || elem.key1 === 'key1-8') {
    removedElements.push(elem);
    return false;
  } else {
    return true;
  }
});

/* Step 3. Add those 3 elements back to the original positions */
removedElements.forEach(elem => {
  finalArr.splice(elem.position - (finalArrOriginalLength - finalArr.length)   1, 0, elem);
});

/* The inserted elements from step 3 are being inserted in the wrong position as seen when this console.log prints out finalArr */
console.log('FINAL ARR', finalArr);

<iframe name="sif1" sandbox="allow-forms allow-modals allow-scripts" frameborder="0"></iframe>

CodePudding user response：

There's no need to subtract from elem.position.

If you sort the removed elements by the original positions, you should be able to insert them at those positions.

This assumes there haven't been any other changes to the array.

// Step 1. Create array of 10 elements
const originalValues = maxAmount => {
  let finalArray = [];
  for (let i = 0; i < maxAmount; i  ) {
    finalArray.push({
      key1: `key1-${i 1}`,
      position: i
    });
  }
  return finalArray;
}
let finalArr = originalValues(10);
const finalArrOriginalLength = finalArr.length;

//Step 2. Remove 3 random elements in this case key1-2, key1-7, key1-8
const removedElements = [];
finalArr = finalArr.filter(elem => {
  if (elem.key1 === 'key1-7' || elem.key1 === 'key1-2' || elem.key1 === 'key1-8') {
    removedElements.push(elem);
    return false;
  } else {
    return true;
  }
});

/* Step 3. Add those 3 elements back to the original positions */
removedElements.sort((a, b) => a.position - b.position).forEach(elem => {
  finalArr.splice(elem.position, 0, elem);
});

console.log('FINAL ARR', finalArr);

<iframe name="sif2" sandbox="allow-forms allow-modals allow-scripts" frameborder="0"></iframe>

CodePudding user response：

Try this...

// Step 1. Create array of 10 elements
const originalValues = maxAmount => {
  let finalArray = [];
  for (let i = 0; i < maxAmount; i  ) {
    finalArray.push({
      key1: `key1-${i 1}`,
      position: i
    });
  }
  return finalArray;
}
let finalArr = originalValues(10);
const finalArrOriginalLength = finalArr.length;

//Step 2. Remove 3 random elements in this case key1-2, key1-7, key1-8
const removedElements = [];
finalArr = finalArr.filter(elem => {
  if (elem.key1 === 'key1-7' || elem.key1 === 'key1-2' || elem.key1 === 'key1-8') {
    removedElements.push(elem);
    return false;
  } else {
    return true;
  }
});

// Step 3. Add those 3 elements back to the original positions

removedElements
.sort((a,b)=>{return a.position > b.position ? 0 : 1 });

removedElements.forEach(elem => {
  finalArr.splice(elem.position, 0, elem);
});

/* The inserted elements from step 3 are being inserted in the wrong position as seen when this console.log prints out finalArr */
console.log('FINAL ARR', finalArr);

<iframe name="sif3" sandbox="allow-forms allow-modals allow-scripts" frameborder="0"></iframe>