Cast Array<Any> to Array<Int> in Swift

Question

I have array of Any objects called timestamps, in which first object is string, and rest objects are Int. What i want is, to drop first element and treat rest of array as Array of Int objects..

I tried:

let timestamps = xAxisData.dropFirst()
if let timestamps = timestamps as? Array<Int> { 
}

It compile, but it says - Cast from 'ArraySlice<Any>' to unrelated type 'Array<Int>' always fails

I could possibly iterate through array and create new temporary array with check every element whether it Int or not, but i think there is a better cleaner way?

"in which first object is string, and rest objects are Int." This indicates you've used the wrong datatype. You meant to use a struct Timestamps { let something: String; values: [Int] } here, not an [Any]. Building things on Any is going to bite you again and again. — Rob Napier
– Rob Napier, Commented Mar 13, 2019 at 17:41

rmaddy · Accepted Answer · 2019-03-13 17:15:43Z

3

You need to create an Array from the ArraySlice created by dropFirst.

let timestamps = Array(xAxisData.dropFirst())
if let timestamps = timestamps as? [Int] { 
}

answered Mar 13, 2019 at 17:15

rmaddy

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Aaron Cyrman · Accepted Answer · 2019-03-14 02:37:43Z

2

I like to use something like a flatMap so no matter were the non-Int values are in the array they are not consider for the resulting array.

let originalArray:[Any] = ["No int", 2, 3, "Also not int", 666, 423]
let intArray:[Int] = originalArray.flatMap { $0 as? Int }
print(intArray)

Will print this:

[2, 3, 666, 423]

So in your case you could do something like:

let timestamps = xAxisData.flatMap { $0 as? Int }

As stated by Steve Madsen in the comment below, if you are using Swift 4.1 or newer Apple suggest to used compactMap for getting rid of optional nils so that specific use of flatMap is deprecated.

let timestamps = xAxisData.compactMap { $0 as? Int }

edited Mar 14, 2019 at 2:37

answered Mar 13, 2019 at 18:26

Aaron Cyrman

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2 Comments

Steve Madsen Over a year ago

Swift 4.1 deprecated the use of flatMap in favor of compactMap to remove optionals from a sequence.

Aaron Cyrman Over a year ago

Thanks Steve, I edited the answer to add your input.

Steve Madsen · Accepted Answer · 2019-03-13 18:21:09Z

1

Here is another method to convert a subset of an array with mixed types to something more specific:

let intArray = anyArray.compactMap { $0 as? Int }

answered Mar 13, 2019 at 18:21

Steve Madsen

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3 Comments

Evgeniy Kleban Over a year ago

not really efficient because i know that first element will be string, your solution is O(n) complexity.

Steve Madsen Over a year ago

True; for your specific use case @rmaddy's solution is more appropriate. In terms of your question's title, though, a more general solution should be useful to others.

dan Over a year ago

An as? cast on an array is O(n) anyway since it has to check every element

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