Je suis novice en F # et j'ai joué avec les dossiers et les ai changés. J'essaie d'appliquer ma propre fonction sans utiliser de carte à ma liste. C'est ce que j'ai jusqu'ici. Je me demande simplement si ma façon d'écrire une cartographie sans utiliser la carte fonctionne correctement.Dossiers F # et mappage
module RecordTypes =
// creation of simple record
// immutable by default - key word mutable allows that to change
type Student =
{
Name : string
mutable age : int
mutable major : string
}
// setting up a few records with student information
// studentFive.age <- studentFive.age + 2 ; example of how to change mutable variable
let studentOne = { Name = "bob" ; age = 20 ; major = "spanish" }
let studentTwo= { Name = "sally" ; age = 18 ; major = "english" }
let studentThree = { Name = "frank" ; age = 22 ; major = "history" }
let studentFour = { Name = "lisa" ; age = 19 ; major = "math" }
let studentFive = { Name = "john" ; age = 17 ; major = "philosophy" }
// placing the records into a lits
let studentList = [studentOne; studentTwo; studentThree ;studentFour; studentFive]
// placing the records into a lits
let studentList = [studentOne; studentTwo; studentThree ;studentFour; studentFive]
// itterate through a list and printing each records
printf "the unsorted list of students: \n"
studentList |> List.iter (fun s-> printf "Name: %s, Age: %d, Major: %s\n" s.Name s.age s.major)
// a sort of the records based on the name, can be sorted by other aspects in the records
let sortStudents alist =
alist
|> List.sortBy (function student -> student.age)
let rec selectionSort = function
| [] -> [] //if the list is empty it will return an empty list
| l -> let min = List.min l in // otherwise set a min variable and use the min function to find the smallest item in a list
let rest = List.filter (fun i -> i <> min) l in // set a variable to hold the rest of the list using filter
// Returns a new collection containing only the elements of the collection for which the given predicate returns true
// fun sets up a lambda expression that if (i -> i <> (not equal boolean) min) if i(the record is not the min put it into a list)
let sortedList = selectionSort rest in // sort the rest of the list that isnt the min
min :: sortedList // :: is an operator that creates a list, left elem appended to right side
let unsortedList = studentList
let sortedList = selectionSort unsortedList
printfn "sorted list based on first name:\n"
sortedList |> List.iter(fun s -> printf "Name: %s, Age: %d, Major: %s\n" s.Name s.age s.major)
ici est où j'ai essayé de créer ma propre carte avec fonction foo
let foo x = x + 1
let applyOnEachElement (list : Student list) (someFunction) =
list |> List.iter(fun s -> someFunction s.age)
//let agedStudents = applyOnEachElement studentList foo
printf " the students before function is applied to each: \n"
sortedList |> List.iter(fun s -> printf "Name: %s, Age: %d, Major: %s\n" s.Name s.age s.major)
printf " the student after function is applied to each: \n"
agedStudents |> List.iter(fun s -> printf "Name: %s, Age: %d, Major: %s\n" s.Name s.age s.major)
Où, dans le code ci-dessus , est-ce que vous essayez d'écrire 'map' sans carte? –
Il serait utile si vous fournissez du code qui * compile * et démontre le problème aussi succinctement que possible. Voir [Comment demander] (http://stackoverflow.com/help/mcve) pour un conseil sur ce sujet. –
BTW, 'map' peut être implémenté dans deux lignes de code - quatre si vous avez besoin d'être récursif de queue. –