How to shift position index in array of object in JavaScript?

Question

I need some help to shift the position index in the array of objects. I am having a bunch of arrays of objects which need to be shifted at index 0 or 1 based on value key.

const arrayObj1 = [
    {
        id: 234,
        value: "FGH"
    },
    {
        id: 454,
        value: "XYZ"
    },
    {
        id: 654,
        value: "ABC"
    },
    {
        id: 543,
        value: "ABC"
    },
]

Let say I have above array of objects, and I want to shift position to index 0, 1 if the value is "ABC". As of now they are positioning at index 2 and 3. So the array of object will be looks like below after shifting their position.

expectedArrayofObj = [
    {
        id: 654,
        value: "ABC"
    },
    {
        id: 543,
        value: "ABC"
    },
    {
        id: 234,
        value: "FGH"
    },
    {
        id: 454,
        value: "XYZ"
    },
]

what is the output if id 654 have value ABC, while 543 have value DEF? — hgb123
– hgb123, Commented Dec 23, 2020 at 5:18

Aliasgher Nooruddin · Accepted Answer · 2020-12-23 05:18:29Z

2

const arrayObj1 = [
  {
    id: 234,
    value: 'FGH',
  },
  {
    id: 454,
    value: 'XYZ',
  },
  {
    id: 654,
    value: 'ABC',
  },
  {
    id: 543,
    value: 'ABC',
  },
]
 
index = arrayObj1 .findIndex(resp => resp.value=='ABC')

arrayObj1 .push(...arrayObj1 .splice(0, index));

console.log(arrayObj1)

answered Dec 23, 2020 at 5:18

Aliasgher Nooruddin

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1 Comment

IvanD Over a year ago

This does not work if ABC objects are all over the place and not in the end.

IvanD · Accepted Answer · 2020-12-23 05:22:43Z

1

const arrayObj1 = [
  {
    id: 234,
    value: 'FGH',
  },
  {
    id: 454,
    value: 'XYZ',
  },
  {
    id: 654,
    value: 'ABC',
  },
  {
    id: 543,
    value: 'ABC',
  },
]

const shift = (arr, value) => {
  const newArr = []

  // Pushing ABC first
  for (const obj of arr) {
    if (obj.value === value) {
      newArr.push(obj)
    }
  }

  // Pushing the rest
  for (const obj of arr) {
    if (obj.value !== value) {
      newArr.push(obj)
    }
  }

  return newArr
}

console.log(shift(arrayObj1, 'ABC'))

If you don't care about the order of other elements, you can use (unstable) sort:

const arrayObj1 = [
  {
    id: 234,
    value: 'FGH',
  },
  {
    id: 454,
    value: 'XYZ',
  },
  {
    id: 654,
    value: 'ABC',
  },
  {
    id: 543,
    value: 'ABC',
  },
]

const shift = (arr, value) => {
  const sortingFunction = (a, _) => (a.value === value ? -1 : +1)
  arrayObj1.sort(sortingFunction)
  return arrayObj1
}

console.log(shift(arrayObj1, 'ABC'))

edited Dec 23, 2020 at 5:22

answered Dec 23, 2020 at 5:14

IvanD

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4 Comments

IvanD Over a year ago

@vickram, I added another solution, which is a bit simpler

makinyelure Over a year ago

He didn't want to sort. He just wanted to swap two items. This can be done in lesser complexity. Your solutions have at least O(n) in time complexity.

IvanD Over a year ago

Yes, the first solution is O(n) time and O(n) space and the second one is O(n logn) time and O(1) complexity, so the second one is slower, but requires no additional memory.

IvanD Over a year ago

Hey @vickram, please accept my solution if it was helpful :)

lissettdm · Accepted Answer · 2020-12-23 13:01:07Z

1

You can use Array.prototype.reduce()

const arrayObj1 = [{id: 234, value: "FGH"},{id: 454,value: "XYZ"},{id: 654,value: "ABC"},{id: 543,value: "ABC"}];

function shiftBy(value) {
  return arrayObj1.reduce((arr, c) => ((c.value===value && [c, ...arr]) || [...arr, c]),[]);
}

console.log(shiftBy("ABC"));

edited Dec 23, 2020 at 13:01

answered Dec 23, 2020 at 12:48

lissettdm

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Comments

makinyelure · Accepted Answer · 2020-12-23 05:36:38Z

0

You can do a swap using the index. Good thing is that we are able to do this in O(1) space complexity and O(n) time complexity based on the number of items in the list. The indexOf kind of increased it.

const SHIFT_BY_VALUE = (val1, val2) => {
    let originIndex = arrayObj1.indexOf(arrayObj1.find(e => e.value == val1));
    let itemToShift = arrayObj1[originIndex];

    let destinationIndex = arrayObj1.indexOf(arrayObj1.find(e => e.value == val2));
    arrayObj1[originIndex] = arrayObj1[destinationIndex];
    arrayObj1[destinationIndex] = itemToShift;
    return arrayObj1; // No need to return, Array is by reference. 
}

answered Dec 23, 2020 at 5:36

makinyelure

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Comments

Himanshu · Accepted Answer · 2020-12-23 17:01:33Z

0

const arrayObj1 = [{
    id: 234,
    value: 'FGH',
  },
  {
    id: 454,
    value: 'XYZ',
  },
  {
    id: 654,
    value: 'ABC',
  },
  {
    id: 543,
    value: 'ABC',
  },
];

let changeValue = 'ABC';

const temp = arrayObj1.filter((item) => item.value === changeValue);
arrayObj1.forEach((item) => {
  if (item.value !== changeValue) temp.push(item);
});
console.log(temp);

const arrayObj1 = [
  {
    id: 234,
    value: 'FGH',
  },
  {
    id: 454,
    value: 'XYZ',
  },
  {
    id: 654,
    value: 'ABC',
  },
  {
    id: 543,
    value: 'ABC',
  },
];

arrayObj1.sort(function (a, b) {
  if (a.value < b.value) return -1;
  else return 1;
  return 0;
});
console.log(arrayObj1);

edited Dec 23, 2020 at 17:01

answered Dec 23, 2020 at 5:47

Himanshu

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2 Comments

IvanD Over a year ago

This does not work if the value that we want in the beginning is not 'ABC' but "XYZ" for example

Himanshu Over a year ago

I have updated for any value present in array ABC,XYZ,...

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