Generate 'nice' numbers for label ticks over a range, such as for y-axis on a chart.
Adapted from pseudo-code in Graphics Gems, Volume 1 by Andrew S. Glassner (1995). See also Tufte (1983) for a discussion of topic.
Available as an open source Swift library to be incorporated in other apps.
SwiftNiceScale is part of the OpenAlloc family of open source Swift software tools.
let ns = NiceScale(105...543, desiredTicks: 5)! print("nice range=\(ns.range)") => "nice range=100.0...600.0" print("tick interval=\(ns.tickInterval)") => "tick interval=100.0" print("labels=\(ns.tickValues)") => "labels=[100.0, 200.0, 300.0, 400.0, 500.0, 600.0]"
ValueRange type is declared within
T is your
BinaryFloatingPoint data type:
typealias ValueRange = ClosedRange<T>
init?(_ rawRange: NiceScale<T>.ValueRange, desiredTicks: Int)- create a new
Initialization will fail and return
nil if provided nonsense parameters, such as a range with zero extent, or a desired tick count less than 2.
The initialization values are also available as properties:
let rawRange: NiceScale<T>.ValueRange - the source range from which to calculate a nice scaling
let desiredTicks: Int - the desired number of ticks in the scaling (default: 10)
Computed properties are lazy, meaning that they are only calculated when first needed.
The basic set of properties...
var range: NiceScale<T>.ValueRange - The calculated ‘nice’ range, which should include the ‘raw’ range used to initialize this object.
var extent: T - The distance between bounds of the range.
var ticks: Int - The number of ticks in the range. This may differ from the
desiredTicks used to initialize the object.
var tickInterval: T - The distance between ticks in the range.
var tickValues: [T] - The values for the ticks in the range.
var tickFractionDigits: Int - Number of fractional digits to show in tick label values.
More specialized properties dealing with positive and negative portions of scale...
var hasNegativeRange: Bool - If true, the range includes negative values.
var hasPositiveRange: Bool - If true, the range includes positive values.
var negativeRange: NiceScale<T>.ValueRange - The portion of the range that is negative.
0…0 if none.
var positiveRange: NiceScale<T>.ValueRange - The portion of the range that is positive.
0…0 if none.
var negativeExtent: T - If there’s a negative portion of range, the distance between its lower bound and 0. A non-negative value.
var positiveExtent: T - If there’s a positive portion of range, the distance between its upper bound and 0. A non-negative value.
var negativeExtentUnit: T? - The negativeExtent, expressed as unit value in the range
var positiveExtentUnit: T? - The positiveExtent, expressed as unit value in the range
func scaleToUnit(T) -> T - Scale value to
0…1 in the range.
func scaleToUnitNegative(T) -> T - Scale value to
0…1 in the negative portion of range, if any.
func scaleToUnitPositive(T) -> T - Scale value to
0…1 in the positive portion of range, if any.
Swift open-source libraries (by the same author):
And commercial apps using this library (by the same author):
Copyright 2021 FlowAllocator LLC
Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at
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Other contributions are welcome too. You are encouraged to submit pull requests to fix bugs, improve documentation, or offer new features.
The pull request need not be a production-ready feature or fix. It can be a draft of proposed changes, or simply a test to show that expected behavior is buggy. Discussion on the pull request can proceed from there.
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