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Merge 2 arrays and created a new one

I have 2 arrays this

let array1 = [
    {
        designation: "SSE",
        emailId: "abc@gmail.com",
        employeeId: 1997,
        firstName: "user2",
    },
    {
        designation: "DEVELOPER",
        emailId: "ab@gmail.com",
        employeeId: 19,
        firstName: "user1",
    },
    {
        designation: "DEVELOPER",
        emailId: "ab@gmail.com",
        employeeId: 191,
        firstName: "user1",
    },
];

let array2 = [
    {
        designation: "SSE",
        emailId: "abc@gmail.com",
        employeeId: 199,
        firstName: "user2",
    },
    {
        designation: "DEVELOPER",
        emailId: "ab@gmail.com",
        employeeId: 19,
        firstName: "user1",
    },
    {
        designation: "DEVELOPER",
        emailId: "ab@gmail.com",
        employeeId: 191,
        firstName: "user1",
    },
    {
        designation: "TESTER",
        emailId: "ab@gmail.com",
        employeeId: 1221,
        firstName: "user1",
    },
];

See, I have some common records in both arrays and one is missing in array2. I want to merge them into one if employeeId doesn't match. Like this.

let array3 = [
   {employeeId: 1997, isActive: false}, 
   {employeeId: 199, isActive: true}, 
   {employeeId: 19, isActive: true}, 
   {employeeId: 191, isActive: true},
   {employeeId: 1221, isActive: false}
]

array3[3].isActive is false because it doesn't match in both arrays.

about 4 years ago · Juan Pablo Isaza

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Answer 1 · 2022-07-05T17:23:04.984Z

Get an array of employeeId from array1
Get an array of employeeId from array2
Create an array with all the (unique) emplyeeId's
Create an array with the ID's that are not matching
map() over all the ids (array_0_ids) to:
1. Create an object
2. Set isActive to the result of !non_matching.includes(emplyeeId)

let array1 = [{designation: "SSE", emailId: "abc@gmail.com", employeeId: 199, firstName: "user2", }, {designation: "DEVELOPER", emailId: "ab@gmail.com", employeeId: 19, firstName: "user1", }, {designation: "DEVELOPER", emailId: "ab@gmail.com", employeeId: 191, firstName: "user1", }, ];
let array2 = [{designation: "SSE", emailId: "abc@gmail.com", employeeId: 199, firstName: "user2", }, {designation: "DEVELOPER", emailId: "ab@gmail.com", employeeId: 19, firstName: "user1", }, {designation: "DEVELOPER", emailId: "ab@gmail.com", employeeId: 191, firstName: "user1", }, {designation: "TESTER", emailId: "ab@gmail.com", employeeId: 1221, firstName: "user1", }, ];

let array_1_ids = array1.map(i => i.employeeId);
let array_2_ids = array2.map(i => i.employeeId);
let array_0_ids = [ ...array_1_ids, ...array_2_ids ].filter((v, i, s) => s.indexOf(v) === i);

let non_matching = array_2_ids.filter(id => !array_1_ids.includes(id));

let result = array_0_ids.map(emplyeeId => {
  return {
    emplyeeId,
    isActive: !non_matching.includes(emplyeeId)
  };
});

console.log(result);

[
  {"emplyeeId": 199, "isActive": true },
  {"emplyeeId": 19, "isActive": true}, 
  {"emplyeeId": 191, "isActive": true},
  {"emplyeeId": 1221, "isActive": false} 
]

Answer 2 · 2022-07-05T17:23:04.992Z

let result = [];

const employeeIdArray2 = array2.map(e => e.employeeId);
const employeeIdArray1 = array1.map(e => e.employeeId);

const missingEmployeeIdArray = employeeIdArray2.length > employeeIdArray1.length ? employeeIdArray1 : employeeIdArray2;

result = array2.map(e => {
  if (missingEmployeeIdArray.includes(e.employeeId)) {
    return {
      ...e,
      isActive: true
    }
  } else {
    return {
      ...e,
      isActive: false
    }
  }
})

Answer 3 · 2022-07-05T17:23:05.003Z

Create an object where the key will be the employeeId and the value will be the number of occurrences
Create the final array by iterating over the object entries, set isActive to true when the number of occurrences is 2.

const array1 = [
  {
    designation: "SSE",
    emailId: "abc@gmail.com",
    employeeId: 199,
    firstName: "user2",
  },
  {
    designation: "DEVELOPER",
    emailId: "ab@gmail.com",
    employeeId: 19,
    firstName: "user1",
  },
  {
    designation: "DEVELOPER",
    emailId: "ab@gmail.com",
    employeeId: 191,
    firstName: "user1",
  },
];

const array2 = [
  {
    designation: "SSE",
    emailId: "abc@gmail.com",
    employeeId: 199,
    firstName: "user2",
  },
  {
    designation: "DEVELOPER",
    emailId: "ab@gmail.com",
    employeeId: 19,
    firstName: "user1",
  },
  {
    designation: "DEVELOPER",
    emailId: "ab@gmail.com",
    employeeId: 191,
    firstName: "user1",
  },
  {
    designation: "TESTER",
    emailId: "ab@gmail.com",
    employeeId: 1221,
    firstName: "user1",
  },
];

const reducer = (acc, e) => ({
  ...acc,
  [e.employeeId]: (acc[e.employeeId] + 1) || 1,
}); 

const arr3 = Object.entries([...array1, ...array2].reduce(reducer, {}))
  .map(([employeeId, count]) => ({ employeeId, isActive: count == 2 }));
  
console.log(arr3);

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Merge 2 arrays and created a new one

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Andres GPT