Get new array of values from within sorted array

Question

I have an array of SCNNode that are sorted by their y positions(Float):

nodesSortedByY = scene.rootNode.childNodes.sorted { $0.position.y > $1.position.y }

What I would like to do is get a new array from nodesSortedByY where the y values are within a certain range in a similar way to how subscript works but by passing actual values not indexes.

For example:

let nodesSortedByY = [5.0, 4.0, 4.0, 3.0, 2.0, 2.0, 1.0]
let subRange = nodesSortedByY(4.0...2.0)
print(subRange) // [4.0, 4.0, 3.0, 2.0, 2.0]

I tried using indexes originally combined with this binary search but it doesnt work if the values dont exist within the array:

let yPositions = nodesSortedByY.map({ $0.position.y })
let firstIndex = yPositions.binarySearch(forFirstIndexOf: firstValue) ?? 0
let lastIndex = yPositions.binarySearch(forLastIndexOf: lastValue) ?? 0
nodesSortedByY[lastIndex...firstIndex]

Are you looking for filter()? let filtered = nodesSortedByY.filter({ (2.0...4.0).contains($0) }) — Larme
– Larme, Commented Oct 22, 2020 at 14:26
Not quite, it would have to be filtered by a range of the nodes y positions somehow? — Wazza
– Wazza, Commented Oct 22, 2020 at 14:30
DIdn't you want to get all the values of "y" if they are between 2.0 and 4.0? That's what's doing the filter. Else, keeping your last idea: let lowerBound = nodesSortedByY.firstIndex(where: { $0 <= 4.0 }) let upperBound = nodesSortedByY.lastIndex(where: { $0 >= 2.0 }) let sub = nodesSortedByY[lowerBound!...upperBound!] — Larme
– Larme, Commented Oct 22, 2020 at 14:33
i want an array of SCNNode still but sorting it by y and getting the the new range array by the nodes y values — Wazza
– Wazza, Commented Oct 22, 2020 at 14:36
I guess so, but the author used map, and simplified his example to [Double], but my solutions should work. — Larme
– Larme, Commented Oct 22, 2020 at 14:37

Larme · Accepted Answer · 2020-10-22 15:37:52Z

1

What you want is to filter().

let sub = nodesSortedByY.filter { (2.0...4.0).contains($0.position.y) }

We keep only the elements in nodesSortedByY where its y position is inside the range [2.0; 4.0].

Since you sorted your array (descending order), you can applied that logic too (modification of your attempt)

let lowerBound = nodesSortedByY.firstIndex(where: { $0 <= 4.0 }) ?? nodesSortedByY.startIndex
let upperBound = nodesSortedByY.lastIndex(where: { $0 >= 2.0 }) ?? nodesSortedByY.endIndex
let sub = nodesSortedByY[lowerBound...upperBound]

edited Oct 22, 2020 at 15:37

answered Oct 22, 2020 at 14:44

Larme

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2 Comments

Wazza Over a year ago

let sub = nodesSortedByY.filter { (2.0...4.0).contains($0.position.y) } works perfectly for me thank you, i didnt realize you could filter like that

Leo Dabus Over a year ago

@Wazza 2.0...4.0 ~= $0.position.y

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