CODEWITHSUNDEEP
iosswiftcastingdoublensobject
vibhu1201
vibhu1201

Reputation: 143

Convert NSObject to double

I have an array that holds the following values: [0.1, 0.2, 0.18, "other"]. I recognize adding the "other" makes this an NSObject array. I want to be able to retrieve the first three values as doubles when they are selected so I can multiply them with other doubles. However, when I try to do it simply, it says "Can not put binary operator * with double and NSObject". How can I typecast or convert the NSObjects to doubles?

Upvotes: 2

Views: 1780

Answers (4)

cojoj
cojoj

Reputation: 6475

You just need to cast it... The simples solution is something like:

let arr: [NSObject] = [0.1, 0.2, 0.18, "other"]
let result = (arr[0] as! Double) * (arr[1] as! Double)

But you should avoid force casting and find some better solution.

You can also flatMap your array and get only proper values in result like: 

let newArr = arr.flatMap { $0 as? Double }

But you have to be careful with this solution as you now depend on Foundation and if you have a slightly different values in array eg. [0.1, 0.2, 0.18, "other", false] you'll get a wrong result.

And adding "other" doesn't qualify this array to be NSObject. It can actually be of Any type as well, but this wont't change anything in case of casting values to proper types, but will add some security and will simplify things cause you won't be dependent on Foundation.

Upvotes: 1

user3441734
user3441734

Reputation: 17534

generally the same result as vacawama's answer has, but without help of Foundation

var myarr: Array<Any> =  [0.1, 0.2, 0.18, "other", true]

for d in myarr {
    if let d = d as? Double {
        print(d)
    }
}

prints

0.1
0.2
0.18

if you need extracted array of doubles, you can use

let doubles = myarr.flatMap { $0 as? Double }
print(doubles)

prints

[0.1, 0.2, 0.18]

declaration var arr: Array<Any> or var arr:[Any] force your code to use pure Swift, even though you have imported Foundation before.

If you need to convert values in your array to Double values (if possible), the easiest way I can see right now (please see vacawama's notes below) is something like 

let myarr:[Any] =  [0.1, 0.2, 0.18, "other", true, 17, "22.3", "-0.2e-1","27"]
let doubles = myarr.flatMap { Double("\($0)") }
print(doubles) // [0.1, 0.2, 0.18, 17.0, 22.3, -0.02, 27.0]

Upvotes: 2

vacawama
vacawama

Reputation: 154583

For your Doubles to be be stored in an array of NSObjects, they are converted to NSNumbers.

If you iterate through your array, selecting values that are NSNumbers using where and assign them to a value which is of type AnyObject, you can call doubleValue on them to retrieve the Double value from the NSNumber:

var myarr =  [0.1, 0.2, 0.18, "other"]

for d:AnyObject in myarr where d is NSNumber {
    print(d.doubleValue * 2)
}

Output:

0.2
0.4
0.36

Explanation:

This works because any object (an instance of a class) can be assigned to a value of type AnyObject, and when AnyObject is used as a concrete value, all known @objc properties and methods are available. Since NSNumber has the doubleValue property, and we have already checked that d is an NSNumber, we can call doubleValue knowing it won't crash at runtime.

Upvotes: 2

Kevin Sylvestre
Kevin Sylvestre

Reputation: 38012

You can force cast using as!:

// let values = [0.1,0.2,0.3,"other"]
let val1 = values[0] as! Double
let val2 = values[1] as! Double
let val3 = values[2] as! Double
let other = values[3] as! String

print(val1 * val1)
print(val2 * val2)
print(val3 * val3)
print(other)

Upvotes: 4

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