Create Vega-Lite visualizations (version 4) in Haskell. https://github.com/DougBurke/hvega

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BSD-3-Clause licensed by Douglas Burke
Maintained by dburke.gw@gmail.com

Module documentation for

This version can be pinned in stack with:hvega-,10921


vega-lite version

Create Vega-Lite visualizations in Haskell. It targets version 4.12 of the Vega-Lite specification. Note that the module does not include a viewer for these visualizations (which are JSON files), but does provide several helper functions, such as toHtmlFile, which create HTML that can be viewed with a browser to display the visualization. Other approaches include automatic display in IHaskell notebooks - with the ihaskell-vega package - or use of external viewers such as Vega View and Vega-Desktop.

It started off being a copy on an early version (2.2.1) of the Elm Vega library, which is released under a BSD3 license by Jo Wood of the giCentre at the City University of London.

This code is released under the BSD3 license.



The Vega-Lite example gallery contain a number of visualizations of the cars.json dataset, which has a number of columns to display, such as “Horsepower”, “Miles_per_Gallon”, and “Origin”. The following code will create a visualization that plots the efficiency of the cars (the “mpg”) as a function of its Horsepower, and color-code by the origin of the car:

let cars =  dataFromUrl "https://vega.github.io/vega-datasets/data/cars.json" []

    enc = encoding
            . position X [ PName "Horsepower", PmType Quantitative ]
            . position Y [ PName "Miles_per_Gallon", PmType Quantitative, PTitle "Miles per Gallon" ]
            . color [ MName "Origin", MmType Nominal ]

    bkg = background "rgba(0, 0, 0, 0.05)"

in toVegaLite [ bkg, cars, mark Circle [MTooltip TTEncoding], enc [] ]

When the JSON is viewed with a Vega-Lite aware viewer, the resultant plot can be interacted with (e.g. to use the tooltip support) using the interactive version. It can also be viewed as a PNG:

Simple scatterplot


In late 2019 and early 2020 the star Betelgeuse - a member of the constellation Orion - dimmed enough that you could see it. Betelgeuse is a member of the class of Red Supergiant stars, which are massive enough that they will go supernova at some point, and so there was some speculation that we could see a “naked-eye” supernova (even though the current models suggest that Betelgeuse has about 100,000 more years to go before this happens). This interest lead to a lot of observations added to the American Association of Variable Star Observers database, which we are going to look at below. This example is rather-more involved than the case one, since it involves data filtering and creation, multiple plots, faceting, and interactive selection.

let titleStr = "Betelegeuse's magnitude measurements, collated by AAVSO"

    w = width 600
    h = height 150

    pos1Opts fld ttl = [PName fld, PmType Quantitative, PAxis [AxTitle ttl]]
    x1Opts = pos1Opts "days" "Days since January 1, 2020"
    y1Opts = pos1Opts "magnitude" "Magnitude" ++ [PSort [Descending], yRange]
    yRange = PScale [SDomain (DNumbers [-1, 3])]

    filtOpts = [MName "filterName", MmType Nominal]
    filtEnc = color (MLegend [ LTitle "Filter", LTitleFontSize 16, LLabelFontSize 14 ] : filtOpts)
              . shape filtOpts

    circle = mark Point [ MOpacity 0.5, MFilled False ]

    encOverview = encoding
                  . position X x1Opts
                  . position Y y1Opts
                  . filtEnc

    selName = "brush"
    pos2Opts fld = [PName fld, PmType Quantitative, PAxis [AxNoTitle],
                   PScale [SDomain (DSelectionField selName fld)]]
    x2Opts = pos2Opts "days"
    y2Opts = pos2Opts "magnitude" ++ [PSort [Descending]]

    encDetail = encoding
                . position X x2Opts
                . position Y y2Opts
                . filtEnc

    xlim = (Number (-220), Number 100)
    ylim = (Number (-0.5), Number 2.5)
    overview = asSpec [ w
                      , h
                      , encOverview []
                      , selection
                        . select selName Interval [ Encodings [ChX, ChY]
                                                  , SInitInterval (Just xlim) (Just ylim)
                        $ []
                      , circle

    detailPlot = asSpec [ w
                        , h
                        , encDetail []
                        , circle

    headerOpts = [ HLabelFontSize 16
                 , HLabelAlign AlignRight
                 , HLabelAnchor AEnd
                 , HLabelPadding (-24)
                 , HNoTitle
                 , HLabelExpr "'Filter: ' + datum.label"

    details = asSpec [ columns 1
                     , facetFlow [ FName "filterName"
                                 , FmType Nominal
                                 , FHeader headerOpts
                     , spacing 10
                     , specification detailPlot

in toVegaLite [ title titleStr [ TFontSize 18 ]
              , dataFromUrl "https://raw.githubusercontent.com/DougBurke/hvega/master/hvega/data/betelgeuse-2020-03-19.json" []
              , transform
                . filter (FExpr "datum.filterName[0] === 'V'")
                . filter (FExpr "datum.magnitude < 4")
                . calculateAs "datum.jd - 2458849.0" "days"
                $ []
              , vConcat [overview, details]
              , configure
                . configuration (Axis [ TitleFontWeight Normal, TitleFontSize 16, LabelFontSize 14 ])
                $ []

This can be viewed as

PNG version of the lightcurve


A tutorial is provided as part of the module: it is based, as is so much of the module, on the Elm Vega walk through. The tutorial is available on hackage - and includes the plot outputs - and the plots it creates are also available by importing the Graphics.Vega.Tutorials.VegaLite module.

The Vega-Lite Example Gallery has been converted to IHaskell notebooks in the notebooks directory. Start with the overview notebook, which describes the set up, and then the individual sections have their own notebooks (with names of VegaLiteGallery-<section>.ipynb.

It is strongly advised that you stick with jupyter notebook rather than jupyter lab, since the 0.3 release of ihaskell-hvega provides much better support for the former than the latter.

The notebooks have been created using Jupyter Lab (thanks to Tweag I/O’s JupyterWith environment).

Differences to Elm Vega

Elm Vega has changed significantly since I started hvega, and no-longer exposes data types directly but uses functions instead: for example, rather than PName, it uses a function like pName. It is an open question whether hvega will make the same switch. Over time the naming of certain operations or data types has diverged between hevga and Elm Vega.

One of the more-obvious changes is that the output of toVegaLite is a separate type from the input values - that is VegaLite and VLSpec - since it makes it easier to display the output of hvega in IHaskell. The JSON specification is retrieved from this type with fromVL. The release adds some more type safety (restricting the functions that can be applied to encoding and transform for instance).


For the latest version of this document, please see https://github.com/DougBurke/hvega/blob/master/hvega/CHANGELOG.md.

The tutorial has been expanded to add a section describing the new pie chart support (the Arc mark).

The introductory text of the module has been updated to start with the “cars” example (from the README) before rampng up to the Betelgeuse example.

The Vega-Lite tests are now validated against version 4.12 of the Vega-Lite schema.

New Constructors

Support for arcs has been added: the Arc type has been added to Mark; Theta, Theta2, R, and R2 have been added to Position; and MInnerRadius, MOuterRadius, MPadAngle, MRadius2, MRadiusOffset, MRadius2Offset, MTheta2, MThetaOffset, and MTheta2Offset added to MarkProperty. ArcStyle has been added to ConfigurationProperty.

Support for ARIA attributes has been added to a number of features (e.g. Aria and AriaDescription for AxisConfig and MAria, MAriaDescription, MAriaRole, MAriaRoleDescription for MarkProperty, AriaStyle for ConfigurationProperty). The ariaDescrption encoding has been added, along with the AriaDescriptionChannel.

The angle encoding channel has been added for text and point marks.

The Channel type has gained ChAngle, ChTheta, ChTheta2, ChRadius, ChRadius’, ‘ChDescription’, and ChURL.

Layers have been added to Arrangement (Layer) and to RepeatFields (LayerFields).

The MRepeatDatum and MDatum, PRepeatDatum and PDatum, and TRepeatDatum and TDatum pairs have been added to MarkChannel, PositionChannel, and TextChannel respectively.

The MarkProperty now has support for labelling the X (or X2) coordinate as the “width” of the plot and Y (or Y2) as the “height” of the plot. See MXWidth, MX2Width, MYHeight, and MY2Height.

Improved support for tick scales: TickCount and TickCountTime have been added to AxisConfig, AxTickCountTime has been added to AxisProperty, LTickCountTime has been added to LegendProperty, and LeTickCountTime has been added to LegendConfig.

Add support for width and height to scale’s range, with the RHeight and RWidth constructors. The RPair constructor has been added as an experimental means for specifying just the minimum and maximum values.

AxisProperty has gained AxFormatAsCustom. AxisConfig has gained Format, FormatAsNum, FormatAsTemporal, and FormatAsCustom. LegendProperty has gained LFormatAsCustom. HeaderProperty has gained HFormatAsCustom. TextChannel has gained TFormatAsCustom. The ConfigurationProperty type has a new option to configure support for custom format types (CustomFormatStyle).

AxisConfig and AxisProperty have gained new cap styles: DomainCap, GridCap, TickCap and AxDomainCap, AxGridCap, AxTickCap respectively.

The TZIndex option of TitleConfig can now be used with TitleStyle (prior to Vega-Lite 4.12 it was only supported when used with title). The LeZIndex type has been added to LegendConfig.

The HyperlinkChannel has gained a number of constructors it was missing: HyBand, HyFormat, HyFormatAsNum, HyFormatAsTemporal, HyFormatAsCustom, HyLabelExpr, HyTitle, and HyNoTitle. A similar update has been made to TextChannel, which has gained TBand and TLabelExpr.

The Vega-Lite tests are now validated against version 4.8 of the Vega-Lite Sschema.

The RepeatStyle constructor for ConfigurationProperty should not be used, as its functionality has been moved to ConcatStyle in Vega-Lite 4.8. This constructor will be removed at some point in the future but is still available (as support for Vega-Lite 4.8 is limited).

Breaking Changes

The HTitleFontWeight constructor (a member of HeaderProperty) now takes a FontWeight argument rather than Text.

The LeTitle constructor from LegendConfig was removed as it is not supported in Vega-Lite (LeNoTitle remains, as it is used to remove legend titles from a visualization).

ScBinLinear was removed from Scale as it is not used by Vega-Lite.

New constructors

The HeaderProperty type has gained the following constructors from Vega-Lite 4.8: HLabelBaseline, HLabelFontWeight, HLabelLineHeight, and HOrient.

The AxisConfig type has gained the Disable constructor from Vega-Lite 4.8.

The LegendConfig type has gained the LeDirection and (from Vega-Lite 4.8) LeDisable constructors. The LegendProperty type has gained LLabelExpr, LSymbolLimit, and LTitleLineHeight constructors.

Minor documentation fixes (typos and fixing links).

The Vega-Lite tests are now validated against version 4.7 of the Vega-Lite schema.

New functionality

The BlendMode type has been added for controlling how marks blend with their background. This is used with the new MBlend constructor for marks.

Breaking Change

The axis style options for specific data- or mark- types (AxisBand, AxisDiscrete, AxisPoint, AxisQuantitative, and AxisTemporal) have been changed to accept an additional argument (the new AxisChoice type) which defines which axis (X, Y, or both) the configuration should be applied to. This is to support new axis configuration options added in Vega-Lite 4.7.0.

The ChTooltip Channel constructor has been removed as support for this channel type was dropped in Vega-Lite 4.

New constructors

The ScaleDomain type has gained DSelectionField and DSelectionChannel constructors, which allow you to link a scale (e.g. an axis) to a selection that is projected over multiple fields or encodings.

The Operation type has gained the Product specifier from Vega-Lite 4.6.0.

The TextChannel has gained TStrings to support multi-line labels.

The VAlign type has gained AlignLineTop and AlignLineBottom (Vega-Lite 4.6.0).

LineBreakStyle has been added to ConfigurationProperty.

The height of multi-line axis labels can now be set with the LabelLineHeight and AxLabelLineHeight properties of the AxisConfig and AxisProperty types (Vega-Lite 4.6.0).

Numeric filter ranges, specified with FRange, can now be lower- or upper-limits - NumberRange and NumberRange respectively - added to the FilterRange type.

The Vega-Lite tests are now validated against version 4.5 of the Vega-Lite schema.

New functionality

New function for use with encoding: strokeDash. The ChStrokeDash constructor has been added to the Channel type, and RNumberLists (Vega-Lite 4.4) to ScaleRange.

Named styles have been added for axes as well as marks. As mentioned below, this involves deprecating the previous constructors for naming styles, as there are now separate configuration options: AxisNamedStyles and MarkNamedStyles. The AStyle and AxStyle options have been added to AxisConfig and AxisProperty respectively. The StyleLabel type alias has been added to help the documentation, but provides no extra type safety.

Breaking changes

The ConcatStyle and FacetStyle constructors for ConfigurationProperty now accept a common type, CompositionConfig, rather than having separate ConcatConfig and FacetConfig types with the same meaning. So ConcatColumns and FColumns have been replaced by CompColumns, and CompSpacing and FSpacing by CompSpacing.

The ViewFill and ViewStroke constructors of ViewConfig no longer take an optional Color argument. The Nothing case has been replaced by new constructors: ViewNoFill and ViewNoStroke.

The VBFill and VBStroke constructors of ViewBackground no longer take an optional Color argument. The Nothing case has been replaced by new constructors: VBNoFill and VBNoStroke.

New constructors

FacetChannel has gained the following constructors: FAlign, FCenter, and FSpacing. The last one would have collides with the FacetStyle option, but this has fortuitously been renamed to CompSpacing.

MSymbol has been added to MarkChannel which can be used to make the shape encoding conditional on a data or selection condition.

The TUStep and TUMaxBins constructors have been added to TimeUnit for controlling how time values are binned.

The MarkProperty type has gained the MCornerRadiusEnd constructor, which is used to draw rounded histogram bars, and MTexts for specifying multiple text values.

Error box and band properties (constructors in MarkProperty) can now be turned off with explicit No variants: MNoBorders, MNoBox, MNoMedian, MNoRule, and MNoTicks. These join the MNoOutliers constructor.

The ScaleProperty type has gained SDomainMid, useful for asymmetric diverging color scales, and SReverse from Vega-Lite v4.5. The ScaleDomain type has gained the DUnionWith option from Vega-Lite v4.3. The ScaleConfig type has gained SCXReverse from Vega-Lite v4.5.

Labels can now be vertically aligned to their baseline with the AlignBaseline constructor of the VAlign type.

Headers (HeaderProperty) have gained the following constructors: HLabel, HLabelExpr, HLabelFontStyle, HTitleFontStyle, and HTitleLineHeight.

Conditional axis (ConditionalAxisProperty) has gained the following constructors for features added in Vega-Lite v4.2 and v4.5: CAxLabelOffset, CAxLabelPadding, and CAxTickSize.

Cursor handling has been enhanced (to match Vega-Lite 4.1): ViewCursor has been added to ViewConfig and SMCursor to SelectionMarkProperty.

The legend configuration has been updated (to match Vega-Lite 4.0) with the addition of LeSymbolLimit, LeTickCount, LeTitleLineHeight, and LeUnselectedOpacity constructors.

The axis configuration and property types (AxisConfig and AxisProperty) have gained the Vega-Lite 4.4 LabelOffset and AxLabelOffset constructors. Note that version 4.4.0 of the Vega-Lite specification has these fields as strings but this is fixed in version 4.5.0.

ConfigurationProperty has added new constructors: AxisDiscrete and AxisPoint from Vega-Lite 4.5, AxisQuantitative and AxisTemporal from Vega-Lite 4.4, BoxplotStyle, ErrorBandStyle, ErrorBarStyle, FontStyle (Vega-Lite 4.3), HeaderColumnStyle, HeaderFacetStyle, HeaderRowStyle, ImageStyle, and RepeatStyle.

Deprecated symbols

ConfigurationProperty has seen a large number of deprecations, as a number of constructors have been renamed:

  • The NamedStyle and NamedStyles have been replaced by MarkNamedStyles;

  • Autosize, Background, CountTitle, FieldTitle, Legend, NumberFormat, Padding, Projection, Range, Scale, TimeFormat, and View constructors have been replaced by AutosizeStyle, BackgroundStyle, CountTitleStyle, FieldTitleStyle, LegendStyle, NUmberFormatStyle, PaddingStyle, ProjectionStyle, RangeStyle, ScaleStyle, TimeFormatStyle, ViewStyle respectively.

Update to version 4.0 of the Vega-Lite specification (tested against version 4.0.2). There are several changes in default behavior due to this (tooltips are now disabled by default, the background now defaults to white rather than transparent), although this is also controlled by how the Vega-Lite visualization is rendered, which can make tracking down why something has changed a bit awkward.

There is more-extensive use of type aliases, such as Color, and the introduction of several more (e.g. DashStyle and FieldName). These do not add any type safety, but help the documentation (as they provide a single place to explain the meaning and any constraints on a particular value). There are some changes that do improve type safety, discussed in the “Breaking changes” section below.

Documentation improvements, including a new section in the tutorial on choropleths contributed by Adam Conner-Sax, and plots using an Aitoff projection contributed by Jo Wood.

New functionality

Title (and subtitle) strings can now be split across multiple lines: use ‘\n’ to indicate a line break.

Colors are now stripped of extraneous white space, and if empty converted to the JSON null value rather than an empty string.

The pivot transform has been added, along with the PivotProperty preferences type. This is the inverse of fold.

The density transform has been added, along with the DensityProperty configuration type, to support kernel density estimation (e.g. to generate a continuous distribtion from a discrete one).

The loess transform has been added, along with the LoessProperty configuration type, to support scatterplot smoothing.

The regression transform has been added, along with the RegressionProperty and RegressionMethod configuration types, to support regression analysis.

The quantile transform has been added, along with the QuantileProperty type, to support quantile analysis.

The url encoding has been added, which allows you to view images (e.g. PNG) via the (new) Image mark type. The MAspect MarkProperty has been added as a configuration option.

The lookupSelection transform has been added to support joining data via a selection. The SelectionLabel type alias has been added to help the documentation.

The heightOfContainer and widthOfContainer functions have been added to support responsive sizing, although I have not had much success in getting them to work!

The tooltip encoding will now turn off tooltips if given an empty list (although note that tooltips are now off by default in Vega-Lite 4).

Breaking changes

The combineSpecs function has been removed.

In an attempt to provide some type safety, the encoding, transform, resolve, selection, and configure functions now take specialised types (EncodingSpec, TransformSpec, ResolveSpec, SelectSpec, and ConfigureSpec respectively) rather than the generic LabelledSpec type. Simple visualizations should remain unchanged, but helper functions may need to have their type signatures updated.

The lookup transform has been changed so that the list of fields stored when the keys match is now specified by the LookupFields type (rather than a list of field names). This supports providing aliases and handling of default values, and now subsumes the lookupAs encoding, which has been marked as deprecated.

The RemoveInvalid constructor has removed from ConfigurationProperty, and has been replaced by the MRemoveInvalid constructor of MarkProperty. The Stack constructor was removed.

The SRangeStep constructor from ScaleProperty has been removed. The widthStep and heightStep functions should be used instead.

The ViewWidth and ViewHeight constuctors of ViewConfig have been replaced by ViewContinuousWidth, ViewContinuousHeight, ViewDiscreteWidth, and ViewDiscreteHeight (well, the symbols remain but have been deprecated for the continous-named versions).

The SCRangeStep and SCTextXRangeStep constructors of ScaleConfig have been removed. The new ViewStep constructor of ViewConfig should be used as a replacement.

The ShortTimeLabels, LeShortTimeLabels, and MShortTimeLabels constructors - from AxisConfig, LegendConfg, and MarkProperty respectively - have been removed.

New constructors

This section does not repeat names mentioned above.

AxisProperty has gained the AxDataCondition constructor for marking a subset of axis properties as being conditional on their position, and the ConditionalAxisProperty for defining which properties (grid, label, and tick) can be used in this way. It has also gained the AxLabelExpr constructor, which allows you to change the content of axis labels, AxTickBand for positioning the labels for band scales (and the associated BandAlign type), AxTitleLineHeight to specify the line height, and AxTranslateOffset for applying a translation offset to the axis group.

AxisConfig has gained TickBand, TitleLineHeight, and TranslateOffset, matching the additions to AxisProperty.

The ViewBackgroundStyle constructor has been added to ViewConfig.

The TitleConfig type gained the following constructors: TAlign, TdX, TdY, TLineHeight, TSubtitle, TSubtitleColor, TSubtitleFont, TSubtitleFontSize, TSubtitleFontStyle, TSubtitleFontWeight, TSubtitleLineHeight, and TSubtitlePadding.

Added AFitX and AFitY constructors to the Autosize type.

The SelectionProperty type has gained the BindLegend constructor, and the associated BindLegendProperty type, to allow selection of a legend (categorical data only).

The TextChannel type has gained the TString constructor, which lets you specify the text content as a literal.

Two new projections - EqualEarth and NaturalEarth1 - have been added to the Projection type.

Support for color gradients has been added for marks via the MColorGradient, MFillGradient, and MStrokeGradient constructors of MarkProperty, along with the new ColorGradient and GradientProperty types for defining the appearance of the gradient. The GradientCoord and GradientStops type aliases have also been added (although they provides no type safety).

The MCornerRadius, MCornerRadiusTL, MCornerRadiusTR, MCornerRadiusBL, and MCornerRadiusBR constructors have been added to MarkProperty to set the corner radii of rectangular marks.

The MDir, MEllipsis, and MLimit constructors have been added to MarkProperty to control how text is truncated. The TextDirection type has been added for use with MDir.

The MarkProperty type has gained MLineBreak and MLineHeight constructors for controlling how multi-line labels are displayed. Note that hvega will always split on the newline character (\n), which will over-ride the MLineBreak setting.

The DTMonthNum and DTDayNum constructors have been added to DateTime.

The BinProperty type has gained the SelectionExtent constructor, for defining a bin range via an interval selection.

The PositionChannel type has gained the PBand constructor, for defining the size of a mark relative to a band, and MarkProperty has added MTimeUnitBand and MTimeUnitBandPosition.

Bug fixes

The selection property SInitInterval Nothing Nothing is now a no-op (as it does nothing), rather than generating invalid JSON.

The following options or symbols generated incorrect JSON output: ONone, LSymbolStrokeWidth, LeLabelOpacity.

Documentation fix (rendering of a URL), provided by Alexey Kuleshevich (lehins). The tests should now build without warning in GHC 8.8.1 (CPP to the rescue again!).

Avoid a build warning about importing <> from Data.Monoid in GHC 8.8.1 by using the CPP sledge-hammer. Relaxed the bounds on containers so that the tests can be built on stack LTS 9.21 (GHC 8.0.2).

Updated the tutorial, adding in a new plot to introduce the addition of a second axis to the visualization (parallaxBreakdown).

Thanks to (in no order): Matthew Pickering (mpickering), Adam Conner-Sax (adamConnerSax), and Jo Wood (jwoLondon).

This is a large release, in that it greatly-improves the functionality of hvega (more-closely aligning it with version 3.4.0 of the Vega-Lite specification), but does provide a number of breaking changes (a number of functions and constructors have either been removed or had some combination of being renamed, argument types have changed, or the number of arguments has been changed). The documentation has also seen a number of additions and improvements.

A large number of functions, data types, and constructors for data types have been added, based on version 1.12.0 (and the development version of the next release) of the elm-vegalite module. Thanks to Jo Wood for doing all the work! The Haddock documentation indicates new symbols with the since label.

Bug fixes

Corrected the serialization of the datasets function, reported by Matthew Pickering as issue 29.

Improved the output to better-match the Vega Lite 3.4.0 specification. Note that hvega does not guarantee that it always creates valid output, in part because this would complicate the API, but also because the Vega-Lite specification is changing (e.g. I reported several issues with version 3.3.0 of the specification during development of this release, some of which have been addressed in the 3.4.0 version).

New functions, symbols, and types

The error-related types and functions discussed below are based on changes provided by Adam Conner-Sax.

toVegaLiteSchema has been added to allow you to specify a different Vega-Lite schema. toVegaLite uses version 3 but version 4 is being worked on as I type this. The vlSchema function has been added, along with vlSchema4, vlSchema3, and vlSchema2 values. The toHtmlWith and toHtmlFileWith functions have been added to support more control over the embedding of the Vega-Lite visualizations, and the versions of the required Javascript libraries used by the toHtmlXXX routines has been updated.

The VLProperty type now exports its constructors, to support users who may need to tweak or augment the JSON Vega-Lite specification created by hvega (see issue 17). It has also gained several new constructors and associated functions, which are given in brackets after the constructor: VLAlign (align); VLBounds (bounds); VLCenter (center, centerRC); VLColumns (columns); VLConcat (vlConcat); VLSpacing (alignRC, spacing, spacingRC); VLUserMetadata (usermetadata); and VLViewBackground (viewBackground). It is expected that you will be using the functions rather the constructors!

The ZIndex type has been added: this provides constructors for the common options - ZFront and ZBack - and a fall-through (ZValue) as a protection against future changes to the Vega-Lite specification.

Four new type aliases have been added: Angle, Color, Opacity, and ZIndex. These do not provide any new functionality but do document intent.

The noData function has been added to let compositions define the source of the data (whether it is from the parent or not), and data sources can be named with dataName. Data can be created with dataSequence, dataSequenceAs, and sphere. Graticules can be created with graticule. The NullValue type has been added to DataValue to support data sources that are missing elements, but for more-complex cases it is suggested that you create your data as an Aeson Value and then use dataFromJson. Support for data imputation (creating new values based on existing data) has been added, as discussed below.

The alignment, size, and composition of plots can be defined and changed with align, alignRC, bounds, center, centerRC, columns, spacing, and spacingRC.

Plots can be combined and arranged with: facet, facetFlow, repeat, repeatFlow, and vlConcat

New functions for use in a transform: flatten, flattenAs, fold, foldAs, impute, and stack.

New functions for use with encoding: fillOpacity, strokeOpacity, strokeWidth,

The ability to arrange specifications has added the “flow” option (aka “repeat”). This is seen in the addition of the Flow constructor to the Arrangement type - which is used with ByRepeatOp, HRepeat, MRepeat, ORepeat, PRepeat, and TRepeat.

The Mark type has gained Boxplot, ErrorBar, ErrorBand, and Trail constructors. The MarkProperty type has gained MBorders, MBox, MExtent, MHeight, MHRef, MLine, MMedian, MOrder, MOutliers, MNoOutliers, MPoint, MRule, MStrokeCap, MStrokeJoin, MStrokeMiterLimit, MTicks, MTooltip, MWidth, MX, MX2, MXOffset, MX2Offset, MY, MY2, MYOffset, and MY2Offset constructors.

The Position type has added XError, XError2, YError, and YError2 constructors.

The MarkErrorExtent type was added.

The BooleanOp type has gained the FilterOp and FilterOpTrans constructors which lets you use Filter expressions as part of a boolean operation. The Filter type has also gained expresiveness, with the FLessThan, FLessThanEq, FGreaterThan, FGreaterThanEq, and FValid.

The Format type has gained the DSV constructor, which allow you to specify the separator character for column data.

The MarkChannel type has been expanded to include: MBinned, MSort, MTitle, and MNoTitle. The PositionChannel type has added PHeight, PWidth, PNumber, PBinned, PImpute, PTitle, and PNoTitle constructors.

The LineMarker and PointMarker types have been added for use with MLine and MPoint respectively (both from MarkProperty).

The ability to define the binning property with binAs, DBin, FBin, HBin, MBin, OBin, PBin, and TBin has been expanded by adding the AlreadyBinned and BinAnchor constructors to BinProperty, as well as changing the Divide constructor (as described below).

The StrokeCap and StrokeJoin types has been added. These are used with MStrokeCap, VBStrokeCap, and ViewStrokeCap and MStrokeJoin, VBStrokeJoin, and ViewStrokeJoin respectively.

The StackProperty constructor has been added with the StOffset and StSort constructors. As discussed below this is a breaking change since the old StackProperty type has been renamed to StackOffset.

The ScaleProperty type has seen significant enhancement, by adding the constructors: SAlign, SBase, SBins, SConstant and SExponent. THe Scale tye has added ScSymLog ScQuantile, ScQuantize, and ScThreshold.

The SortProperty type has new constructors: CustomSort, ByRepeatOp, ByFieldOp, and ByChannel. See the breaking-changes section below for the constructors that were removed.

The AxisProperty type has seen significant additions, including: AxBandPosition, AxDomainColor, AxDomainDash, AxDomainDashOffset, AxDomainOpacity, AxDomainWidth, AxFormatAsNum, AxFormatAsTemporal, AxGridColor, AxGridDash, AxGridDashOffset, AxGridOpacity, AxGridWidth, AxLabelAlign, AxLabelBaseline, AxLabelNoBound, AxLabelBound, AxLabelBoundValue, AxLabelColor, AxLabelNoFlush, AxLabelFlush, AxLabelFlushValue, AxLabelFlushOffset, AxLabelFont, AxLabelFontSize, AxLabelFontStyle, AxLabelFontWeight, AxLabelLimit, AxLabelOpacity, AxLabelSeparation, AxTickColor, AxTickDash, AxTickDashOffset, AxTickExtra, AxTickMinStep, AxTickOffset, AxTickOpacity, AxTickRound, AxTickWidth, AxNoTitle, AxTitleAnchor, AxTitleBaseline, AxTitleColor, AxTitleFont, AxTitleFontSize, AxTitleFontStyle, AxTitleFontWeight, AxTitleLimit, AxTitleOpacity, AxTitleX, and AxTitleY.

The AxisConfig has seen a similar enhancement, and looks similar to the above apart from the constructors do not start with ‘Ax’.

The LegendConfig type has been significantly expanded and, as discussed in the Breaking Changes section, changed. It has gained: LeClipHeight, LeColumnPadding, LeColumns, LeGradientDirection, LeGradientHorizontalMaxLength, LeGradientHorizontalMinLength, LeGradientLength, LeGradientOpacity, LeGradientThickness, LeGradientVerticalMaxLength, LeGradientVerticalMinLength, LeGridAlign, LeLabelFontStyle, LeLabelFontWeight, LeLabelOpacity, LeLabelOverlap, LeLabelPadding, LeLabelSeparation, LeLayout, LeLeX, LeLeY, LeRowPadding, LeSymbolBaseFillColor, LeSymbolBaseStrokeColor, LeSymbolDash, LeSymbolDashOffset, LeSymbolDirection, LeSymbolFillColor, LeSymbolOffset, LeSymbolOpacity, LeSymbolStrokeColor, LeTitle, LeNoTitle, LeTitleAnchor, LeTitleFontStyle, LeTitleOpacity, and LeTitleOrient.

The LegendOrientation type has gained LOTop and LOBottom.

The LegendLayout and BaseLegendLayout types are new, and used with LeLayout to define the legent orient group.

The LegendProperty type gained: LClipHeight, LColumnPadding, LColumns, LCornerRadius, LDirection, LFillColor, LFormatAsNum, LFormatAsTemporal, LGradientLength, LGradientOpacity, LGradientStrokeColor, LGradientStrokeWidth, LGradientThickness, LGridAlign, LLabelAlign, LLabelBaseline, LLabelColor, LLabelFont, LLabelFontSize, LLabelFontStyle, LLabelFontWeight, LLabelLimit, LLabelOffset, LLabelOpacity, LLabelOverlap, LLabelPadding, LLabelSeparation, LRowPadding, LStrokeColor, LSymbolDash, LSymbolDashOffset, LSymbolFillColor, LSymbolOffset, LSymbolOpacity, LSymbolSize, LSymbolStrokeColor, LSymbolStrokeWidth, LSymbolType, LTickMinStep, LNoTitle, LTitleAlign, LTitleAnchor, LTitleBaseline, LTitleColor, LTitleFont, LTitleFontSize, LTitleFontStyle, LTitleFontWeight, LTitleLimit, LTitleOpacity, LTitleOrient, LTitlePadding, LeX, and LeY.

Projection has gained the Identity constructor. The ProjectionProperty type has gained PrScale, PrTranslate, PrReflectX, and PrReflectY. The GraticuleProperty type was added to configure the appearance of graticules created with graticule.

The CompositionAlignment type was added and is used with align, alignRC, LeGridAlign, and LGridAlign.

The Bounds type was added for use with bounds.

The ImputeProperty and ImMethod types were added for use with impute and PImpute.

The ScaleConfig type has gained SCBarBandPaddingInner, SCBarBandPaddingOuter, SCRectBandPaddingInner, and SCRectBandPaddingOuter.

The SelectionProperty type has gained Clear, SInit, and SInitInterval.

The Channel type has gained: ChLongitude, ChLongitude2, ChLatitude, ChLatitude2, ChFill, ChFillOpacity, ChHref, ChKey, ChStroke, ChStrokeOpacity. ChStrokeWidth, ChText, and ChTooltip.

The TitleConfig type has gained: TFontStyle, TFrame, TStyle, and TZIndex.

The TitleFrame type is new and used with TFrame from TitleConfig.

The ViewBackground type is new and used with viewBackground.

The ViewConfig type has gained ViewCornerRadius, ViewOpacity, ViewStrokeCap, ViewStrokeJoin, and ViewStrokeMiterLimit.

The ConfigurationProperty type, used with configuration, has gained ConcatStyle, FacetStyle, GeoshapeStyle, HeaderStyle, NamedStyles, and TrailStyle constructors.

The ConcatConfig type was added for use with the ConcatStyle, and the FacetConfig type for the FacetStyle configuration settings.

The HeaderProperty type has gained: HFormatAsNum, HFormatAsTemporal, HNoTitle, HLabelAlign, HLabelAnchor, HLabelAngle, HLabelColor, HLabelFont, HLabelFontSize, HLabelLimit, HLabelOrient, HLabelPadding, HTitleAlign, HTitleAnchor, HTitleAngle, HTitleBaseline, HTitleColor, HTitleFont, HTitleFontSize, HTitleFontWeight, HTitleLimit, HTitleOrient, and HTitlePadding.

The HyperlinkChannel type has gained HBinned.

The FacetChannel type has gained FSort, FTitle, and FNoTitle.

The TextChannel type has gained TBinned, TFormatAsNum, TFormatAsTemporal, TTitle, and TNoTitle.

The TooltipContent type was added, for use with MTooltip.

The Symbol type has gained: SymArrow, SymStroke, SymTriangle, SymTriangleLeft, SymTriangleRight, and SymWedge.

Breaking Changes

Some of these are repeated from above.

The title function now takes a second argument, a list of TitleConfig values for configuring the appearance of the title.

The SReverse construtor was removed from ScaleProperty as it represented a Vega, rather than Vega-Lite, property. The xSort constructors are used to change the order of an item (e.g. PSort, MSort).

The ScSequential constructor was removed from Scale as ScLinear should be used.

The SortProperty type has had a number of changes: the Op, ByField, and ByRepeat constructors have been removed, and ByRepeatOp, ByFieldOp, and ByChannel constructors have been added.

The AxTitleMaxLength and TitleMaxLength constructors have been removed (from AxisProperty and AxisConfig respectively) as they are invalid. The AxTitleLimit (new in this release) and TitleLimit constructors should be used instead.

AxisProperty: the AxValues constructor has been changed from accepting a list of doubles to DataValues. The AxDates constructor has been deprecated and AxValues should be used instead.

There have been significant changes to the LegendConfig type: the EntryPadding, GradientHeight, GradientLabelBaseline, GradientWIdth, and SymbolColor constructors have been removed; the renaming constructors have been renamed so they all begin with Le (e.g. Orient is now LeOrient, and Orient has been added to AxisConfig); and new constructors have been added.

The StackProperty type has been renamed to StackOffset and its constructors have changed, and a new StackProperty type has been added (that references the StackOffset type).

The Average constructor of Operation was removed, and Mean should be used instead.

The LEntryPadding constructor of LegendProperty was removed.

The arguments to the MDataCondition, TDataCondition, and HDataCondition constructors - of MarkChannel, TextChannel, and HyperlinkChannel respectively - have changed to support accepting multiple expressions.

The MarkOrientation type has been renamed Orientation.

The constructors of the ViewConfig type have been renamed so they all begin with View (to match ViewWidth and ViewHeight).

The constructors of the ProjectionProperty type have been renamed so that they begin with Pr rather than P (to avoid conflicts with the PositionChannel type).

The Divide constructor of BinProperty now takes a list of Doubles rather than two.

The TitleConfig type has gained the following constructors: TFontStyle, TFrame, TStyle, and TZIndex. The TitleFrame type was added for use with TFrame.

The ArgMax and ArgMin constructors of Operation now take an optional field name, to allow them to be used as part of an encoding aggregation (e.g. with PAggregate).

The “z index” value has changed from an ‘Int’ to the ‘ZIndex’ type.

The constructors for the Symbol type now all start with Sym, so Cross, Diamond, TriangleUp, TriangleDown, and Path have been renamed to SymCross, SymDiamond, SymTriangleUp, SymTriangleDown, and SymPath, respectively.

The Legend type has been renamed LegendType and its constructors have been renamed ‘GradientLegend’ and ‘SymbolLegend’.

Improved testing

Added a test suite based on the Elm Vega-Lite tests (based entirely on the work of Jo Wood).

The IPython notebooks have been expanded to cover recent changes in the Vega-Lite gallery, and include validation of the output (to check against the expected output).

The minimum base version has been bumped from 4.7 to 4.9, which means ghc 8.0 or later. This is because the release does not appear to build with ghc 7.10. If this restriction is a problem then please comment on the issues list.

There have been minor documentation updates, adding @since annotations.

The Channel type has been extended to include ChFill and ChStroke constructors and the tooltips function allows you to provide multiple tooltips for a channel. The schema version has been changed from 2 to 3, but there has been limited checking to see if the API correctly reflects the new schema.

This functionality was provided by Adam Massmann (massma) and BinderDavid.

Added the toHtml and toHtmlFile functions which create the necessary HTML to view the Vega-Lite visualization using Vega Embed (this is similar to how ihaskell-hvega works).

This functionality was provided by Gregory Schwartz; apologies for taking so long to get it released.

The constructors for the LegendOrientation type have been renamed (by adding the prefix LO) which avoids the name clash with Left and Right seen in earlier releases. This is a breaking API change.

Clarify how to use the library in the main hvega module.

Thanks to contributions from Nicolas Mattia (nmattia) and Marco Zocca (ocramz).

The only change is to the cabal file, where cabal-version: >=1.18 has been changed to cabal-version: 1.18.

Updated the upper bounds of aeson to really allow v1.4. This was not released on Hackage.

Updated the upper bounds of aeson from v1.2 to v1.4.

The cabal package now includes stack.yaml and default.nix (although the latter is not guaranteed to be correct), as well as a change log and an extra image.

This is the initial version of hvega, which is based on version 2.2.1 of the Elm Vega library.