Filter a list based on a parameter - scala

Question

I want to filter the employees based on name and return the id of each employee
case class Company(emp:List[Employee])
case class Employee(id:String,name:String)
val emp1=Employee("1","abc")
val emp2=Employee("2","def")
val cmpy= Company(List(emp1,emp2))
val a = cmpy.emp.find(_.name == "abc")
val b = a.map(_.id)
val c = cmpy.emp.find(_.name == "def")
val d = c.map(_.id)
println(b)
println(d)
I want to create a generic function that contains the filter logic and I can have different kind of list and filter parameter for those list
Ex employeeIdByName which takes the parameters
Updated
criteria for filter eg :_.name and id
list to filter eg:cmpy.emp value
for comparison eg :abc/def
Any better way to achieve the result
I have used map and find

Answer 1

If you really want a "generic" filter function, that can filter any list of elements, by any property of these elements, based on a closed set of "allowed" values, while mapping results to some other property - it would look something like this:
def filter[T, P, R](
list: List[T], // input list of elements with type T (in our case: Employee)
propertyGetter: T => P, // function extracting value for comparison, in our case a function from Employee to String
values: List[P], // "allowed" values for the result of propertyGetter
resultMapper: T => R // function extracting result from each item, in our case from Employee to String
): List[R] = {
list
// first we filter only items for which the result of
// applying "propertyGetter" is one of the "allowed" values:
.filter(item => values.contains(propertyGetter(item)))
// then we map remaining values to the result using the "resultMapper"
.map(resultMapper)
}
// for example, we can use it to filter by name and return id:
filter(
List(emp1, emp2),
(emp: Employee) => emp.name, // function that takes an Employee and returns its name
List("abc"),
(emp: Employee) => emp.id // function that takes an Employee and returns its id
)
// List(1)
However, this is a ton of noise around a very simple Scala operation: filtering and mapping a list; This specific usecase can be written as:
val goodNames = List("abc")
val input = List(emp1, emp2)
val result = input.filter(emp => goodNames.contains(emp.name)).map(_.id)
Or even:
val result = input.collect {
case Employee(id, name) if goodNames.contains(name) => id
}
Scala's built-in map, filter, collect functions are already "generic" in the sense that they can filter/map by any function that applies to the elements in the collection.

Answer 2

You can use Shapeless. If you have a employees: List[Employee], you can use
import shapeless._
import shapeless.record._
employees.map(LabelledGeneric[Employee].to(_).toMap)
To convert each Employee to a map from field key to field value. Then you can apply the filters on the map.