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added DataApproximator+N extension (ChartsOrg#2848)
* added DataApproximator+N extension * fixed PR notes
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,152 @@ | ||
| // | ||
| // DataApproximator+N.swift | ||
| // Charts | ||
| // | ||
| // Created by M Ivaniushchenko on 9/6/17. | ||
| // Licensed under Apache License 2.0 | ||
| // | ||
| // https://github.com/danielgindi/Charts | ||
| // | ||
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| import Foundation | ||
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| extension CGPoint { | ||
| fileprivate func distanceToLine(from linePoint1: CGPoint, to linePoint2: CGPoint) -> CGFloat { | ||
| let dx = linePoint2.x - linePoint1.x | ||
| let dy = linePoint2.y - linePoint1.y | ||
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| let dividend = fabs(dy * self.x - dx * self.y - linePoint1.x * linePoint2.y + linePoint2.x * linePoint1.y) | ||
| let divisor = sqrt(dx * dx + dy * dy) | ||
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| return dividend / divisor | ||
| } | ||
| } | ||
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| private struct LineAlt { | ||
| let start: Int | ||
| let end: Int | ||
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| var distance: CGFloat = 0 | ||
| var index: Int = 0 | ||
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| init(start: Int, end: Int, points: [CGPoint]) { | ||
| self.start = start | ||
| self.end = end | ||
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| let startPoint = points[start] | ||
| let endPoint = points[end] | ||
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| guard (end > start + 1) else { | ||
| return | ||
| } | ||
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| for i in start + 1 ..< end { | ||
| let currentPoint = points[i] | ||
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| let distance = currentPoint.distanceToLine(from: startPoint, to: endPoint) | ||
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| if distance > self.distance { | ||
| self.index = i | ||
| self.distance = distance | ||
| } | ||
| } | ||
| } | ||
| } | ||
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| extension LineAlt: Comparable { | ||
| static func ==(lhs: LineAlt, rhs: LineAlt) -> Bool { | ||
| return (lhs.start == rhs.start) && (lhs.end == rhs.end) && (lhs.index == rhs.index) | ||
| } | ||
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| static func <(lhs: LineAlt, rhs: LineAlt) -> Bool { | ||
| return lhs.distance < rhs.distance | ||
| } | ||
| } | ||
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| extension DataApproximator { | ||
| /// uses the douglas peuker algorithm to reduce the given arraylist of entries to given number of points | ||
| /// More algorithm details here - http://psimpl.sourceforge.net/douglas-peucker.html | ||
| @objc open class func reduceWithDouglasPeukerN(_ points: [CGPoint], resultCount: Int) -> [CGPoint] | ||
| { | ||
| // if a shape has 2 or less points it cannot be reduced | ||
| if resultCount <= 2 || resultCount >= points.count | ||
| { | ||
| return points | ||
| } | ||
| var keep = [Bool](repeating: false, count: points.count) | ||
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| // first and last always stay | ||
| keep[0] = true | ||
| keep[points.count - 1] = true | ||
| var currentStoredPoints = 2 | ||
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| var queue = [LineAlt]() | ||
| let line = LineAlt(start: 0, end: points.count - 1, points: points) | ||
| queue.append(line) | ||
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| repeat { | ||
| let line = queue.popLast()! | ||
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| // store the key | ||
| keep[line.index] = true | ||
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| // check point count tolerance | ||
| currentStoredPoints += 1 | ||
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| if (currentStoredPoints == resultCount) { | ||
| break; | ||
| } | ||
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| // split the polyline at the key and recurse | ||
| let left = LineAlt(start: line.start, end: line.index, points: points) | ||
| if (left.index > 0) { | ||
| self.insertLine(left, into: &queue) | ||
| } | ||
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| let right = LineAlt(start: line.index, end: line.end, points: points) | ||
| if (right.index > 0) { | ||
| self.insertLine(right, into: &queue) | ||
| } | ||
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| } while !queue.isEmpty | ||
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| // create a new array with series, only take the kept ones | ||
| let reducedEntries = points.enumerated().flatMap { (index: Int, point: CGPoint) -> CGPoint? in | ||
| return keep[index] ? point : nil | ||
| } | ||
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| return reducedEntries | ||
| } | ||
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| // Keeps array sorted | ||
| private static func insertLine(_ line: LineAlt, into array: inout [LineAlt]) { | ||
| let insertionIndex = self.insertionIndex(for: line, into: &array) | ||
| array.insert(line, at: insertionIndex) | ||
| } | ||
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| private static func insertionIndex(for line: LineAlt, into array: inout [LineAlt]) -> Int { | ||
| var indices = array.indices | ||
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| while !indices.isEmpty { | ||
| let midIndex = indices.lowerBound.advanced(by: indices.count / 2) | ||
| let midLine = array[midIndex] | ||
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| if midLine == line { | ||
| return midIndex | ||
| } | ||
| else if (line < midLine) { | ||
| // perform search in left half | ||
| indices = indices.lowerBound..<midIndex | ||
| } | ||
| else { | ||
| // perform search in right half | ||
| indices = (midIndex + 1)..<indices.upperBound | ||
| } | ||
| } | ||
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| return indices.lowerBound | ||
| } | ||
| } | ||
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