Get uncommon elements from two list - KOTLIN

Question

I have two list of same model class (STUDENT), sample student object structure is given below,

{   "_id": "5a66d78690429a1d897a91ed",   "division": "G",   "standard": "X",   "section": "Secondary",   "lastName": "Sawant",   "middleName": "Sandeep",   "firstName": "Shraddha",   "pin": 12345,   "isEditable": true,   "isTracked": false } 

One list have 3 objects and other 2. lets say, List A has 1, 2, 3 students and List B has 1, 2

So my question is there any inbuilt functions to get the uncommon element by comparing just the id? If not how can i solve this issue.

FYI, following are the two approaches i have made to solve, but failed miserably.

Approach 1.

internal fun getDistinctStudents(studentsList: List<Students>, prefStudents: List<Students>): List<Students> {     val consolidated = prefStudents.filter {         prefStudents.any { students: Students -> it._id == students._id }     }     return prefStudents.minus(consolidated) } 

Approach 2.

internal fun getDistinctStudents(studentsList: List<Students>, prefStudents: List<Students>): List<Students> {     val consolidatedStudents = studentsList + prefStudents     val distinctStudents = consolidatedStudents.distinctBy{ it._id }     return prefStudents.minus(distinctStudents) } 

Any kind of help will be greatly appreciated.

Thanks

Answer 1

A more Kotlin way to achieve what Ahmed Hegazy posted. The map will contain a list of elements, rather than a key and count.

Using HashMap and Kotlin built-ins. groupBy creates a Map with a key as defined in the Lambda (id in this case), and a List of the items (List for this scenario)

Then filtering out entries that have a list size other than 1.

And finally, converting it to a single List of Students (hence the flatMap call)

val list1 = listOf(Student("1", "name1"), Student("2", "name2")) val list2 = listOf(Student("1", "name1"), Student("2", "name2"), Student("3", "name2"))  val sum = list1 + list2 return sum.groupBy { it.id }     .filter { it.value.size == 1 }     .flatMap { it.value }