Chart

A haskell Charting library targetting SVG.

Usage

>>> :set -XOverloadedLabels
>>> :set -XOverloadedStrings
>>> import Chart
>>> import Optics.Core
>>> let lines = [[Point 0.0 1.0, Point 1.0 1.0, Point 2.0 5.0],[Point 0.0 0.0, Point 2.8 3.0],[Point 0.5 4.0, Point 0.5 0]]
>>> let styles = (\c -> defaultLineStyle & #color .~ palette1 c & #size .~ 0.015) <$> [0..2]
>>> let cs = zipWith (\s x -> LineChart s [x]) styles lines
>>> let lineExample = mempty & #charts .~ named "line" cs & #hudOptions .~ defaultHudOptions :: ChartSvg
>>> writeChartSvg "other/usage.svg" lineExample

Overview

Charting consists of three tightly-coupled domains:

1. data domain: the data to be represented.
2. screen syntax: the syntactics of the data. How and where data is to be represented on a screen (or page), and.
3. the hud: visual aids that help interpret the screened data; such as axes, gridlines and titles.

What is a Chart?

A Chart in this library consists of a specification of the first two items in the above list; data and its syntax.

Here's some data; three lists of points that form lines to be charted:

>>> let lines = [[Point 0.0 1.0, Point 1.0 1.0, Point 2.0 5.0],[Point 0.0 0.0, Point 2.8 3.0],[Point 0.5 4.0, Point 0.5 0]]

and some line styles with different colors in order to distinguish the data:

>>> let styles = (\c -> defaultLineStyle & #color .~ palette1 c & #size .~ 0.015) <$> [0..2]
>>> styles
[LineStyle {size = 1.5e-2, color = Colour 0.02 0.73 0.80 1.00, linecap = Nothing, linejoin = Nothing, dasharray = Nothing, dashoffset = Nothing},LineStyle {size = 1.5e-2, color = Colour 0.02 0.29 0.48 1.00, linecap = Nothing, linejoin = Nothing, dasharray = Nothing, dashoffset = Nothing},LineStyle {size = 1.5e-2, color = Colour 0.66 0.07 0.55 1.00, linecap = Nothing, linejoin = Nothing, dasharray = Nothing, dashoffset = Nothing}]

This is enough to create the charts.

>>> let cs = zipWith (\s x -> LineChart s [x]) styles lines
>>> let lineExample = mempty & #charts .~ named "line" cs & #hudOptions .~ defaultHudOptions :: ChartSvg
>>> :t lineExample
lineExample :: ChartSvg

writeChartSvg "other/usage.svg" lineExample

Hud

Axes, titles, tick marks, grid lines and legends are chart elements that exist to provide references to help explain the data being represented. The collective noun used by the library for these elements is hud. Hud elements can usually be distinguished from data syntax, but need information from the chart domain (data domain and style domain) to function. A tick mark and tick value on an axis need to know the range of the data to be placed properly on the screen. A chart border needs to know the syntactic range of the entire data representation inclusive of representational artifacts that might extend beyond the data domain (A circle glyph representing a point has dimension).

Apart from this functional usage, however, hud elements are pretty much the same as data elements. They are typically composed of the same stuff; rectangles and lines and text and colors.

Given this similarity, the library process for chart creation is roughly:

• collect the chart data and syntax (or style) into a collection of charts (a list or a tree). See Chart and ChartTree
• measure the range of the data values
• fold hud elements into a chart, creating new ChartTree from the hud, keeping track of chart dimensions across three domains:
• The domain of the underlying data
• The domain of the canvas where the data is being represented
• The domain of the chart, inclusive of Hud or decorative elements.

This process is reified in runHudWith. The most common Hud concepts, such as axes and titles, have been collected into the HudOptions type.

An important quality of runHud (and conversion of charts to svg in general) is that this is the point at which chart data is converted from the data domain to the page domain.

Optics Usage

Usage suggests the use of optics-core and OverloadedLabels, but this is not required. Chart, HudOptions and associated chart configuration types are big and sometimes deep syntax trees, and simple optics getting, setting and modding makes manipulation more pleasant. Lens works as well, and the library is perfectly capable of being used with records.

Lenses are supplied, for the optics-core library, but can be easily modified for lens. The chart-svg convention is that lenses are either OverloadedLabels, or suffixed with a single quote '.

Re-exports

module Chart.Primitive

module Chart.Data

module Chart.Hud

module Chart.Style

module Chart.Svg

module Chart.Bar

module Chart.Surface

module Data.Colour

module Data.FormatN

module Data.Path

module Data.Path.Parser