Array filteration and Extraction of data and append to new Array

Question

I have an array with nested array

I want the data to append in a new array.

For the data extraction or filtration what method's i have to use, using library such as lodash

DATA

[ 
    [ 
        {
            _id: 588d9b8a608f2a66c298849f,
            email: 'sd@',
            password: '$2a$10$6..L3c3tANi6ydt9gZbc1O6prPfUd3RB.ner5lilxRyEwo1lPsSoC',
            isJobSeeker: true,
            __v: 0,
            lastName: 'shrestha',
            firstName: 'manish',
            isSeeker: true 
        }
    ],
    [ 
        { 
            _id: 588dbb4f7a48ce0d26cb99fd,
            jobId: [Object],
            seekerId: 588d9b8a608f2a66c298849f,
            employerId: 588d7d6c0ec4512feb819825,
            __v: 0,
        }
    ]
]

REQUIRED DATA

[
    { 
        _id: 588d9b8a608f2a66c298849f,
        email: 'sd@',
        password: '$2a$10$6..L3c3tANi6ydt9gZbc1O6prPfUd3RB.ner5lilxRyEwo1lPsSoC',
        isJobSeeker: true,
        __v: 0,
        lastName: 'shrestha',
        firstName: 'manish',
        isSeeker: true 
    },
    jobId: [{}, {}, {}] // ARRAY WITH OBJECTS
]

also i want to change the jobId key to other key of custom string as jobs

---

Following is my attempt:

console.log('Data filteration', data);
const filteredData = [];
filteredData.push(data[0][0]);
data[1].forEach((i) => {
  filteredData[0].jobs = i.jobId
});
console.log('filteredData', filteredData);

Answer 1

First you should clean you data to have a better structure.

[
  [
    { ... }
  ],
  [
    { ... }
  ]
]

In this datastructure, its difficult to understand what does inner arrays signify. Instead you should use an object. That would define the purpose of array and make your code more readable.

var data=[[{_id:"588d9b8a608f2a66c298849f",email:"sd@",password:"$2a$10$6..L3c3tANi6ydt9gZbc1O6prPfUd3RB.ner5lilxRyEwo1lPsSoC",isJobSeeker:!0,__v:0,lastName:"shrestha",firstName:"manish",isSeeker:!0}],[{_id:"588dbb4f7a48ce0d26cb99fd",jobId:["test","test1"],seekerId:"588d9b8a608f2a66c298849f",employerId:"588d7d6c0ec4512feb819825",__v:0}]];

var cleanedData = {
  userData: data[0],
  userJobMap: data[1],
}

var result = cleanedData.userData.reduce(function(p,c){
  if(c.isJobSeeker){
    var job = cleanedData.userJobMap.filter(x=> x.seekerId === c._id);
    // To copy object and not reference
    var t = Object.assign({}, c, { jobId: job[0].jobId });
    p.push(t)
  }
  return p
}, [])

console.log(result)

References

• Array.map is a tool that iterates over all elements and return different value say a single property of return double value of all numbers in array. Note, this will yield an array of same size.
• Array.filter on the other hand is use to filter array based on condition. This will return a subset of original data but elements will be same. You cannot change element structure.
• Array.reduce is a tool that address cases where you need to return selected elements with parsed value. You can achieve same by chaining .filter().map() but then its an overkill as it would result in O(2n).
• Object.assign In JS objects are passed by reference. So if you assign an object to a variable, you are not copying entire object, but only reference. So it you change anything in this variable, it will also reflect in original object. To avoid this, you need to copy value. This is where Object.assign comes. Note, its not supported by old browsers. For them you can check following post - What is the most efficient way to deep clone an object in JavaScript?

Note: All array functions are part of functional programming paradigm and are used to make your code more readable and concise but they come at an expense of performance. Traditional for will always perform faster then them. So if you want to focus on performance, always try to use for (though difference is very small but can add up for multiple cases and become substantial)