How to insert item at certain positions in a multiple array loop

Question

I'm looping over the following array of arrays and for the first item in the array, I need to insert an object after every item, except the first and maybe last item. The data looks like this...

const data = [
  ['Path', 'Item1', 'Item2', 'Item3', 'Item4', 'Item5', 'Score'],
  ['/path-one', 1, 3, 2, 2, 4,  3],
  ['/path-two', 4, 5, 5, 5, 6, 3],
  ['/path-three', 5, 5, 3, 5, 3, 3],
  ['/path-four', 2, 3, 4, 2, 2, 3],
]

For the first row, except the first item and last item, after every other item I want to insert an object {role: 'annotation'}. For the rest of the rows, for every index in the first item array that has the role object, I want to duplicate the previous value such that if the first array after modification is: ['Path', 'Item1', {role: 'annotation'}, 'Item2', {role: 'annotation'}, 'Score'], then the other arrays will follow the pattern ['/path-one', 'value1', 'value1', 'value2', 'value2', 'value3']

My solution so far has been inadequate. Here's what I came up with...

let indexes = []
let scoreIndex
const result = data.map((item, index) => {
  let clone = [...item]
  item.map((i, ix) => {
    if (index === 0) {
      if (ix !== 0 && typeof clone[ix + 1] === 'string' && typeof clone[ix] !== 'object') {
        if (clone[ix + 1] === 'Score') {
          scoreIndex = ix
        }
        indexes.push(ix)
        clone.splice((ix + 1), 0, {role: 'annotation'})
      }
      return i
    } else {
      if (indexes.includes(ix) && ix !== scoreIndex) {
        item.splice((ix + 1), 0, i)
        return i
      }
      return i
    }
  })
  return clone
})

Your help would be greatly appreciated.

Rickard Elimää · Accepted Answer · 2021-07-29 21:18:45Z

Perhaps I misunderstood something. I assumed the following:

:: The lengths of each array in the data array are the same.

:: You need to inject after each position, which will mess up a for loop that increase it's i(teration) variable.

:: There is always a Path and a Score in the first array.

:: You want to add a new value after each value, apart from the two above.

Solution

Get the length of each array: data[0].length
Loop from the end.
Ignore last position.
Ignore the first position
Splice different value based on if it's the first item in the data array.

I loop over each value once, but I do it in the order of: 'Item5', 4, 6, 3, 3, 'Item4', 2, 5, 5, 2, 'Item3', ...

const data = [
  ['Path', 'Item1', 'Item2', 'Item3', 'Item4', 'Item5', 'Score'],
  ['/path-one', 1, 3, 2, 2, 4,  3],
  ['/path-two', 4, 5, 5, 5, 6, 3],
  ['/path-three', 5, 5, 3, 5, 3, 3],
  ['/path-four', 2, 3, 4, 2, 2, 3],
]

function mapArray(data) {
  let secondToLastItem = data[0].length - 2; // 1 & 3
  let FIRST_ITEM = 0; // 4

  for (let index = secondToLastItem; index > FIRST_ITEM; index--) { // 2
    for (let item = 0; item < data.length; item++) {
      let injectedValue = (item == FIRST_ITEM)  // 5
          ? {'role': 'annotation'}
          : data[item][index]; 
      
      data[item].splice(index + 1, 0, injectedValue);
    }
  }
  
  return data;
}

console.log( mapArray(data) );

aksappy · Accepted Answer · 2021-07-29 21:13:41Z

This answer is not perfect, but should give an idea on how this can solved.

  const data = [
  ['Path', 'Item1', 'Item2', 'Item3', 'Item4', 'Item5', 'Score'],
  ['/path-one', 1, 3, 2, 2, 4,  3],
  ['/path-two', 4, 5, 5, 5, 6, 3],
  ['/path-three', 5, 5, 3, 5, 3, 3],
  ['/path-four', 2, 3, 4, 2, 2, 3],
]
  let indexes = []
let scoreIndex

// This method takes in an error and perform splice with the value passed, if no value passed, it will use the current index value.
const splicer = (arr, index, value) => {
  var length = (arr.length - 1) * 2;
  for(let i = 1; i < length; i = i+2) {
    if(value) {
      arr.splice(i, 0, value);
    } else {
      arr.splice(i, 0, arr[i]);
    }
  }
  return arr;
}

// This method goes through data (array of arrays) and call splicer
const output = data.map((item, index) => {
  if(index == 0) {
    splicer(item, 0, {role : "annotation"})
  } else {
    splicer(item, 0);
  }
});

Output

["Path",{"role":"annotation"},"Item1",{"role":"annotation"},"Item2",{"role":"annotation"},"Item3",{"role":"annotation"},"Item4",{"role":"annotation"},"Item5",{"role":"annotation"},"Score"]
["/path-one",1,1,3,3,2,2,2,2,4,4,3,3]
["/path-two",4,4,5,5,5,5,5,5,6,6,3,3]
["/path-three",5,5,5,5,3,3,5,5,3,3,3,3]
["/path-four",2,2,3,3,4,4,2,2,2,2,3,3]

With map, it is a little tough to skip values (it should be possible), so have used a plan for loop.

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