How to combine objects in an array by condition in Swift?

Question

I have an array of objects:

struct Person {
    let name: String
    let dateOfBirth: Date
    let money: Double
}

It contains people and how much money they have received or spent. The array contains 54 such objects. I need to find all objects with the same name and date fields and sum their money. That is, in the end, I have to get less than 54 records in my array.

Example: In the array, there are 3 records with the object John. For example, first, he received $15.0, then spent $7.0, and then received $4.0. For my task, I need to have 1 record in the array instead of 3 (with money filed as $12.0)

Does anyone have any idea?

(offtopic) I really recommend to represent money values with Decimal not with a Double, otherwise you will start losing precision when summing values. — Sulthan
– Sulthan, Commented Jul 27, 2017 at 14:20
@Sulthan, thanks for the advice, but it is just an example, I do not use it — Alexander Spirichev
– Alexander Spirichev, Commented Aug 2, 2017 at 9:38

David Pasztor · Accepted Answer · 2017-07-27 14:09:42Z

2

You can loop through the array and add them to a dictionary, where the name concatenated with the date of birth will be the key and the sum of the money will be the value.

Assuming your array containing Person objects is called people:

var moneyDictionary = [String:Double]()
for person in people {
    let personKey = "\(person.name)\(person.dateOfBirth)"
    if let personRecord = moneyDictionary[personKey] {
        moneyDictionary[personKey] = personRecord + person.money
    } else {
        moneyDictionary[personKey] = person.money
    }
}

answered Jul 27, 2017 at 14:09

David Pasztor

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Comments

Nagra · Accepted Answer · 2017-07-27 14:31:12Z

0

Maybe something like this would work:

struct Person {
    let name: String
    let dateOfBirth: Date
    let money: Double
}

let currentDate = Date()
let person = Person(name: "James", dateOfBirth: currentDate, money: 15)
let person1 = Person(name: "James", dateOfBirth: currentDate, money: -7)
let person2 = Person(name: "James", dateOfBirth: currentDate, money: 4)

// array of person objects
let personArray = [person, person1, person2]

// selected person
let selectedPerson = person

// filter with selected person only
var matchingPersons = personArray.filter {
    $0.name == selectedPerson.name && $0.dateOfBirth == selectedPerson.dateOfBirth
}

// extract values
var values = matchingPersons.map { $0.money }

// total
var total = values.reduce(0, +)

edited Jul 27, 2017 at 14:31

answered Jul 27, 2017 at 14:24

Nagra

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2 Comments

Sulthan Over a year ago

By the way, you can compare Date instances simply by ==.

Nagra Over a year ago

Updated my answer with regards to @Sulthan comment 👍🏼

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