JavaScript: check if duplicate key values exist in array of objects, if there are, rename it

Question

I have an array "source"

source : [
{
    "id": 1,
    "secondId": 1
},
{
    "id": 2,
    "secondId": 1
},
{
    "id": 3,
    "secondId": 1
}
]

I want to rename the secondId when there are duplicate like this:

[
{
    "id": 1,
    "secondId": 1
},
{
    "id": 2,
    "secondId": 1_2
},
{
    "id": 3,
    "secondId": 1_3
}
]

I have this so far:

for (i = 0 ; i < source.length ; i++) {
  for (j = 0 ; j < source.length ; j++){

    if (source[i]["id"] != source[j]["id"] && source[i]["secondId"] === source[j]["secondId"]){
        source[j]["secondId"] += "_" + (i+1);
    }
    console.log(source[j]["secondId"]);

  }
}

and I'm getting:

[
{
    "id": 1,
    "secondId": 1
},
{
    "id": 2,
    "secondId": 1_2
},
{
    "id": 3,
    "secondId": 1_2_3
}
]

I tried to use some:

if(source[j]["secondId"].includes("_"+ (i+1))){
    console.log(source[j]["secondId"].split("_"+ (i+1)).shift());
}

but I'm getting:

"secondId": 1 "secondId": 1 "secondId": 1_2

How can I do it? Any tips please?

Is the ID a string or a number? Because it's awfully weird to de-duplicate by turning 1 into 12 and 13 and so on... — k.tten
– k.tten, Commented Mar 18, 2022 at 14:51
There are numbers, for the example I put small number but secondId could be bigger. I try to renamed it with "_", so it could be 436_1 and 436_2 when there are duplicate secondId — Gron465
– Gron465, Commented Mar 18, 2022 at 14:56
But... the _ doesn't do anything in numbers! 1_2 is the same thing as 12, and 436_1 is the same thing as 4361. I'm asking what's the reason behind de-duplicating them like this. — k.tten
– k.tten, Commented Mar 18, 2022 at 14:58
Specifically, I guess, when you can already identify an object by its unique id why would you need to change the second id? — Andy
– Andy, Commented Mar 18, 2022 at 15:04
@Andy it's like "id" would be for a category and "secondId" for products (but the products could be of different colors) — Gron465
– Gron465, Commented Mar 18, 2022 at 15:21

James · Accepted Answer · 2022-03-18 15:01:40Z

2

A version using Array.reduce:

let source = [
{
    "id": 1,
    "secondId": 1
},
{
    "id": 2,
    "secondId": 1
},
{
    "id": 3,
    "secondId": 1
}];

let output = Object.values(
  source.reduce((a, e, i) => {
    let testId = e.secondId.toString();
    if (a[testId]) {
      testId = testId.split("_")[0] + "_" + (i + 1);
    }
    a[testId] = {...e, secondId: testId};
    return a;
  }, {})
);

console.log(output);

answered Mar 18, 2022 at 15:01

James

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Comments

jsN00b · Accepted Answer · 2022-03-18 15:10:44Z

This may be a solution to achieve the (assumed) desired objective:

Code Snippet

const markDupes = arr => (
  arr.reduce(
    (fin, {id, secondId}) => ({
      tm: {
        [secondId]: (fin.tm[secondId] || 0) + 1
      },
      newArr: [
        ...fin.newArr,
        {id, secondId: secondId.toString() + (
          fin.tm[secondId] > 0 ? `_${fin.tm[secondId]+1}` : ''
        )}
      ]
    }),
    { tm: {}, newArr: [] }
  )?.newArr
);


const source = [{
    "id": 1,
    "secondId": 1
  },
  {
    "id": 2,
    "secondId": 1
  },
  {
    "id": 3,
    "secondId": 1
  }
];


console.log(markDupes(source));

Explanation

Use .reduce to iterate over the array of objects
Set up an initial fin object with two props tm (tracking-map) and newArr (the result-array which will have the secondId updated as desired)
For each object, destructure to directly access id and secondId
Update the map tm based on the secondId with a counter
Append to the newArr an object with id and secondId props with the latter (secondId) being converted to a string to store values of the format 1_2, 1_3, etc

NOTE: This may not be an optimal solution.

joel n · Accepted Answer · 2022-03-18 15:30:00Z

When you convert 1 to 1_2 or 1_3 it is converting a number to a string which will be a huge pain when you have a use for the number later. Instead what i have done is convert that number to a decimal for as 1.2 ,1.3 which means you can do all sorts of computation on a number without much conversion

let source = [
    {
        "id": 1,
        "secondId": 1
    },
    {
        "id": 2,
        "secondId": 1
    },
    {
        "id": 3,
        "secondId": 1
    }
];

let val = {};
for (const i in source) {
    let v = source[i].secondId
    val[v] = val[v] ? val[v] : v
    if (val[v] !== 1) {
        console.log(source[i].id, v);
        source[i].secondId = Number(v.toFixed(2)) + (val[v] * 0.1)
    }
    val[v]++
}
console.log(source);

if you are really kean of using string instead use source[i].secondId = v+'_'+val[v] instead inside the if by changing the original source json object as well

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