How to modify an array of objects if two following objects have different value?

Question

Consider this array:

const arr = [
  {order: 1, mess:"test1"},
  {order: 2, mess:"test2"},
  {order: 2, mess:"test2"},
  {order: 2, mess:"test2"},
  {order: 3, mess:"test3"},
  {order: 4, mess:"test4"},
]

arr is always sorted by order.

I want to modify it to get:

const arr = [
  {order: 1, mess:"test1"},

  {order: 2, mess:"test2", sep:true},
  {order: 2, mess:"test2"},
  {order: 2, mess:"test2"},

  {order: 3, mess:"test3", sep:true},

  {order: 4, mess:"test4", sep:true},
]

sep must be inserted into an object if it has an order different from the preceding object.

I'm unable to write this function, even if it might be quite simple (I guess!).
At this time, I have this, but it doesn't work at all and I don't understand its behavior.

const arr = [
  {order: 1, mess: "test1"},
  {order: 2, mess: "test2"},
  {order: 2, mess: "test2"},
  {order: 2, mess: "test2"},
  {order: 3, mess: "test3"},
  {order: 4, mess: "test4"},
  ]


arr.forEach(function(value, i) {
  i = Number(i)
  const y = i + 1
  if (arr[i] !== undefined && arr[y] !== undefined) {
    if (arr[i].order === arr[y].order) arr[y].sep = true;
  }
});

console.log(arr)

Do you have any idea? Thanks

i = Number(i) is not necessary

mplungjan
– mplungjan

2022-04-08 11:20:00 +00:00
Commented Apr 8, 2022 at 11:20 — mplungjan
– mplungjan, Commented Apr 8, 2022 at 11:20

Nina Scholz · Accepted Answer · 2022-04-08 11:04:49Z

3

You could map a new array and check the item and the predecessor.

const
    data = [{ order: 1, mess: "test1" }, { order: 2, mess: "test2" }, { order: 2, mess: "test2" }, { order: 2, mess: "test2" }, { order: 3, mess: "test3" }, { order: 4, mess: "test4" }],
    result = data.map((o, i, a) => i && a[i - 1].order !== o.order
        ? { ...o, sep: true }
        : o
    );

console.log(result);

.as-console-wrapper { max-height: 100% !important; top: 0; }

answered Apr 8, 2022 at 11:04

Nina Scholz

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Comments

sandarshnaroju · Accepted Answer · 2022-04-08 11:13:48Z

2

Try this

const arr = [
  {order: 1, mess: "test1"},
  {order: 2, mess: "test2"},
  {order: 2, mess: "test2"},
  {order: 2, mess: "test2"},
  {order: 3, mess: "test3"},
  {order: 4, mess: "test4"},
  ]

arr.forEach((obj,index)=>{
  if(index>0 && obj.order != arr[index-1]['order']){
    arr[index]['sep']=true
  }
});
console.log(arr)

answered Apr 8, 2022 at 11:13

sandarshnaroju

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2 Comments

mplungjan Over a year ago

why not arr[index-1].order no need for the bracket notation

sandarshnaroju Over a year ago

yes, simple dot notation will also work.

mplungjan · Accepted Answer · 2022-04-08 12:48:44Z

0

Simplest change of existing array

const arr = [{ order: 1, mess: "test1" }, { order: 2, mess: "test2" }, { order: 2, mess: "test2" }, { order: 2, mess: "test2" }, { order: 3, mess: "test3" }, { order: 4, mess: "test4" }];

arr.forEach((value, i) => {
  if (i && arr[i-1].order !== arr[i].order) arr[i].sep = true;
});
console.log(arr)

edited Apr 8, 2022 at 12:48

answered Apr 8, 2022 at 11:05

mplungjan

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1 Comment

charnould Over a year ago

Works like a charme and change the current array! Thx.

Yuriy Lug · Accepted Answer · 2022-04-08 11:14:04Z

0

Changes original array:

arr.forEach((el, idx) => {
  if (idx === 0) {
    el.sep = true;
  } else {
    if (el.order !== arr[idx-1].order) {
      el.sep = true;
    }
  }
})

answered Apr 8, 2022 at 11:14

Yuriy Lug

518 bronze badges

Comments

Bilal Ahmad · Accepted Answer · 2022-04-08 13:12:44Z

0

Below is another way to achieve the same result as you want.

I believe a more generalized way.

arr.forEach((obj, index) => {
  
  if(JSON.stringify(obj[index+1]) === JSON.stringify(obj[index+2])) {
    obj[index].sep = true;
  }
})

answered Apr 8, 2022 at 13:12

Bilal Ahmad

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Comments

mplungjan · Accepted Answer · 2022-04-08 11:09:11Z

-1

You can copy the array:

let arr2 = [...arr];

Shift it (so the first item is the second one!)

arr2.shift()

Loop over both

const arr = [{ order: 1, mess: "test1" }, { order: 2, mess: "test2" }, { order: 2, mess: "test2" }, { order: 2, mess: "test2" }, { order: 3, mess: "test3" }, { order: 4, mess: "test4" }];
let arr2 = [...arr];
arr2.shift();
const result = [arr[0]];
let sep = true;
for (const [v1, v2] of [arr, arr2]) if (v1.order===v2.order) result.push(v2); else result.push({...v2, sep})
console.log(result)

edited Apr 8, 2022 at 11:09

mplungjan

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answered Apr 8, 2022 at 11:05

dasfacc

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1 Comment

mplungjan Over a year ago

That does not seem to work all the way

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