How to use the reduce function on array of custom Object in Swift

Question

Considering a Swift Object class Sheep having a simple property var position: CGRect

class Sheep {
    var position: CGRect

    init() {
        position = CGRectZero
    }
}

In an array of Sheep Array<Sheep> How can I get the Sheep with the highest position.origin.y?

I tried the following but got an error: could not find member y

func firstSheep(sheeps: Array<Sheep>) -> Sheep
{
     return sheeps.reduce(sheeps[0]) {max($0.position.origin.y, $1.position.origin.y)}
}

All classes import

import Foundation
import QuartzCore

drewag · Accepted Answer · 2014-07-07 18:36:48Z

2

max is going to return a CGFloat (whichever y is greater). Instead you want to return the sheep that has the highest y value:

return sheeps.reduce(sheeps[0]) {
    ($0.position.origin.y > $1.position.origin.y) ? $0 : $1
}

But be careful because this method will throw a runtime error if sheeps is nil. I would make the return value optional and do the following:

func firstSheep(sheeps: [Sheep]) -> Sheep?
{
    let initial : Sheep? = nil
    return sheeps.reduce(initial) {
        if !$0 {
            return $1
        }
        return ($0!.position.origin.y > $1.position.origin.y) ? $0 : $1
    }
}

You need to setup initial as a separate variable to massage the generic in reduce to be correct.

edited Jul 7, 2014 at 18:36

answered Jun 15, 2014 at 22:54

drewag

95.1k28 gold badges142 silver badges131 bronze badges

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

7 Comments

Nicolas Manzini Over a year ago

i get however the error: Type '($T14, $T18)' does not conform to protocol 'LogicValue'

drewag Over a year ago

@NicolasManzini are you sure you copied exactly? I ran this code in a playground just fine

Nicolas Manzini Over a year ago

indeed NO :) i didn't copy exactly I made a mistake somewhere

drewag Over a year ago

@NicolasManzini Also be careful that this function will throw a runtime error if sheeps does not contain at least one sheep

Nicolas Manzini Over a year ago

yes i was trying to figure out how I could nil the default parameter and return a Sheep? var

|

Collectives™ on Stack Overflow

How to use the reduce function on array of custom Object in Swift

1 Answer 1

7 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

7 Comments

Your Answer

Sign up or log in

Post as a guest

Related