Counting number of same values in a struct array

Question

Had a search here but most answers seem to relate to Boolean values. I have a struct defined and initialised as below:

Struct Question {
   var subjectID: Int
   var questionID: Int
}

//Examples
let questionOne = Question(subjectID: 0, questionID: 0)
let questionTwo = Question(subjectID: 0, questionID: 1)
let questionThree = Question(subjectID: 0, questionID: 2)
let questionFour = Question(subjectID: 1, questionID: 0)

//An array populated with the above
var questions = [Question]()

I would like to find how to calculate:

1) The number of unique subjectID values in questions Array. Answer should be 2.

2) The number of questions in questions Array where subjectID == 0, or 1. Answer should be [3, 1].

I have explored with .filter and .map but perhaps I'm on the wrong tangent? Thanks

Eilon · Accepted Answer · 2020-02-07 18:03:29Z

1

For 1) you would manually filter out duplicate values. You can get an array of all the subjectIDs with .map like so:

let subjectIDs = questions.map { $0.subjectID }

For 2), you can simply use the .filter function like so:

let subjectIdXCount = questions.filter { $0.subjectID == x }.count

answered Feb 7, 2020 at 18:03

Eilon

3,0123 gold badges20 silver badges38 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Tom Over a year ago

Thanks for the reply but the first part (.map) doesn't filter out duplicates, it returns an array of [0, 0, 0, 1]. The second part works great though, thanks!

Eilon Over a year ago

Yep, I said you will have to manually remove the duplicates. This thread might help you with that: stackoverflow.com/questions/25738817/…

Leo Dabus · Accepted Answer · 2020-02-07 18:38:49Z

1

You should use collection's reducemethod and increase the initialResult in case nextPartialResult meets your criteria:

struct Question {
   var subjectID: Int
   var questionID: Int
}

let questionOne = Question(subjectID: 0, questionID: 0)
let questionTwo = Question(subjectID: 0, questionID: 1)
let questionThree = Question(subjectID: 0, questionID: 2)
let questionFour = Question(subjectID: 1, questionID: 0)

let questions = [questionOne, questionTwo, questionThree, questionFour]

let subjectCount = questions.reduce(0) { $0 + ($1.subjectID == 0 ? 1 : 0 )}

print(subjectCount)  // 3

answered Feb 7, 2020 at 18:38

Leo Dabus

237k61 gold badges512 silver badges624 bronze badges

Collectives™ on Stack Overflow

Counting number of same values in a struct array

2 Answers 2

2 Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

2 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related