How do I convert array to an array object and combine two arrays to a one array?

Question

const absentStudentsId = [78, 15, 41, 30] // ======> [{stdId: 78, isPresent: false}, {stdId: 15, isPresent: false}, {stdId: 41, isPresent: false}, {stdId: 30, isPresent: false}]

const presentStudentsId = [80, 61] // ======> [{stdId: 80, isPresent: true}, {stdId: 61, isPresent: true}]

const students = [
  { stdId: 78, isPresent: false },
  { stdId: 15, isPresent: false },
  { stdId: 41, isPresent: false },
  { stdId: 30, isPresent: false },
  { stdId: 80, isPresent: true },
  { stdId: 61, isPresent: true },
]

I want to implement that logic as you see in the commented line.

Nina Scholz · Accepted Answer · 2021-06-21 08:50:52Z

8

You could take a closure over isPresent and map new objects.

const
    buildObject = isPresent => stdId => ({ stdId, isPresent }),
    absentStudentsId = [78, 15, 41, 30],
    presentStudentsId = [80, 61],
    students = [
        ...absentStudentsId.map(buildObject(false)),
        ...presentStudentsId.map(buildObject(true))
    ];
    
console.log(students);

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

answered Jun 21, 2021 at 8:50

Nina Scholz

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2 Comments

Sinan Yaman Over a year ago

Great answer, can you explain buildObject = isPresent => stdId => ({ stdId, isPresent }), this line? I am guessing isPresent is the false or true you passed inside buildObject and stdId is passed by the map function itself?

VLAZ Over a year ago

@SinanYaman correct. It's a curried function

Tushar Shahi · Accepted Answer · 2021-06-21 08:51:24Z

1

.map() -> loop over array elements and return a new item for eachitem with your desired computation.

...(Spread) -> spread operator which expands an array into individual elements.

let ans = [...(absentStudentsId.map(x => { return { stdId : x, present : false} })),...(presentStudentsId.map(x => {return { stdId : x, present : true} }))]

answered Jun 21, 2021 at 8:51

Tushar Shahi

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Comments

Shyam · Accepted Answer · 2021-06-21 08:51:43Z

1

const absentStudentsId = [78, 15, 41, 30] // ======> [{stdId: 78, isPresent: false}, {stdId: 15, isPresent: false}, {stdId: 30, isPresent: false}]

const presentStudentsId = [80, 61] // ======> [{stdId: 80, isPresent: true}, {stdId: 61, isPresent: true}]

const transformStudents = (students, isPresent) => students.map(studentId => ({ stdId: studentId, isPresent}));

const allStudents = [...transformStudents(absentStudentsId, false), ...transformStudents(presentStudentsId, true)];

console.log(allStudents)

answered Jun 21, 2021 at 8:51

Shyam

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Comments

jboockmann · Accepted Answer · 2021-06-21 08:53:37Z

1

Yet another straightforward solution:

const absentStudentsId = [78, 15, 41, 30]
const presentStudentsId = [80, 61]

const students = []
absentStudentsId.forEach(id => students.push({stdID: id, isPresent: false}))
presentStudentsId.forEach(id => students.push({stdID: id, isPresent: true}))

console.log(students)
/*
[
  { stdID: 78, isPresent: false },
  { stdID: 15, isPresent: false },
  { stdID: 41, isPresent: false },
  { stdID: 30, isPresent: false },
  { stdID: 80, isPresent: true },
  { stdID: 61, isPresent: true }
]
*/

answered Jun 21, 2021 at 8:53

jboockmann

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