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added DataApproximator+N extension #2848
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Original file line number | Diff line number | Diff line change |
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// | ||
// 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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The algorithm shouldn't be overridden.
@objc public static func reduceWithDouglasPeukerN(_ points: [CGPoint], resultCount: Int) -> [CGPoint]
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Agree, but in current code there is
@objc open class func reduceWithDouglasPeuker(_ points: [CGPoint], tolerance: CGFloat) -> [CGPoint]
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That should be changed too. This is fine then. I will change to static in a separate PR.