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Javascript – Shift object to last index of an array

Let’s say I have this array of objects:

var array = [
    {
        "identifier": "A",
    },
    {
        "identifier": "B",
    },
    {
        "identifier": "C",
    },
    {
        "identifier": "D",
    },
]

How can I map/reduce this array to get this result:

var array = [
    {
        "identifier": "A",
    },
    {
        "identifier": "C",
    },
    {
        "identifier": "D",
    },
    {
        "identifier": "B",
    },
]

In other words, how can I put "B" at the end of array no matter how large the array is?

array.map((o) => {
  if (o.identifier === 'B') {
     // do what here?
  }
 return o;
})
Tags:

6

Answers


  1. 0

    Start by finding the index where identifier == "B", then splice the array at that index (this returns an array of the deleted item(s), then push the removed item(s) to the end of the original array.

    var array = [{
    "identifier": "A",
  },
  {
    "identifier": "B",
  },
  {
    "identifier": "C",
  },
  {
    "identifier": "D",
  },
]
const bIndex = array.findIndex(arr => (arr.identifier == "B"));
const removed = array.splice(bIndex,1);
array.push(...removed);
console.log("resorted array",array)
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  2. 0

    For mapping (i.e. creating a new array), you can concatenate the slices (before, after, itself):

    const array = [{identifier:"A"},{identifier:"C"},{identifier:"D"},{identifier:"B"}];

const i = array.findIndex(o => o.identifier === 'X');
const result = i < 0 ? [...array]
                     : [...array.slice(0, i), ...array.slice(i+1), array[i]];
console.log(result);

    If you are really looking for a solution that uses the map method, then use the index parameter that the map-callback gets:

    const array = [{identifier:"A"},{identifier:"C"},{identifier:"D"},{identifier:"B"}];

let move = null;
const result = array.map((o, i, array) => {
    if (o.identifier === 'B') move = o;
    return array[i + !!move] ?? move;
});
console.log(result);
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  3. 0

    var given_array = [ { "identifier": "A" }, { "identifier": "B" }, { "identifier": "C" }, { "identifier": "D" } ]; const index = array.findIndex(o => o.identifier === ‘B’); if(!index ==-1){ const item.splice(index, 1); given_array.push(item); console.log(given_array)

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  4. 0

    You could take a generator and delay the wanted item.

    function* moveToEnd(array, identifier) {
    let last = [];
    
    for (const element of array)
        if (element.identifier === identifier) last.push(element);
        else yield element;
        
    yield* last;
}

const
    array = [{ identifier: "A" }, { identifier: "B" }, { identifier: "C" }, { identifier: "D" }],
    result = [...moveToEnd(array, 'B')];

console.log(result);
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  5. 0

    You can achieve the desired result in one simple Array.prototype.sort() call, with a very simple sort predicate.

    In the example I’ve shortened identifier to id to make the code more readable.

    const arr = [{"id": "A"},{"id": "B"},{"id": "C"},{"id": "D"}];

const sortedArr = arr.sort(
  (a, b) => a.id === 'B' 
              ? 1 
              : b.id === 'B' 
                ? -1 
                : 0
);

console.log(sortedArr);
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  6. 0

    As @jonrsharpe pointed out, you can apply sort():

    const array = [
  {
    identifier: 'A',
  },
  {
    identifier: 'B',
  },
  {
    identifier: 'C',
  },
  {
    identifier: 'D',
  },
];
array.sort((a, b) => (b.identifier === 'B' ? -1 : 0));
console.log(array);
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