hvega

Contains the hvega module for creating Vega-Lite visualizations in Haskell, and the ihaskell-hvega module for viewing these visualizations in IHaskell notebooks, although circa June 2021 the IHaskell integration is not as seamless as I'd like.

This code is released under the BSD3 license.

Package: hvega

See the hvega README for more details than given here.

Create Vega-Lite visualizations in Haskell. It targets version 4.15 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.

The hvega package started of as an almost-direct copy of version 2.2.1 of the Elm Vega library, which was released under a BSD3 license by Jo Wood of the giCentre at the City University of London. The two have diverged somewhat since (mainly that hvega still uses data types as its primary control structure whilst the Elm version has moved to functions).

Example

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" ]

    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:

Package: ihaskell-hvega

See the ihaskell-hvega README for more details than given here.

View Vega-Lite visualizations created by the hvega package in IHaskell notebooks.

When used with Jupyter notebooks it relies on Vega-Embed to do the hard work of parsing and displaying the Vega Lite specification.

If run in a Jupyter Lab then the native Vega support is used for displaying the Vega Lite specifications. I recommend using Tweag I/O's jupyterWith environment to set this up, and have a rudimentary shell.nix example in the notebooks directory.

How do I create a visualization?

The hvega package allows you to create a visualization but this is just a JSON file - you still need a way to view it. There are a number of ways:

• view it in the Vega Editor (although this is easiest for small JSON files)
• embed the file into a HTML page and use the Vega Embed Javascript library to view it
• the hvega package contains helper routines that will create a HTML page that includes Vega Embed for viewing in a web browser (see toHtmlFile and related routines)
• use a "Vega viewer" - I have a Haskell-based version at Vega View but there are alternatives, such as vega desktop.

The Vega-Lite ecosystem page contains a miriad useful links.

Installation

The packages are available on hackage:

• hvega
• ihaskell-hvega

There is a top-level stack.yaml which builds both hvega and ihaskell-hvega using Stack. There is also a default.nix file for development with Nix - you can try

% nix-build
... wait an indeterminite time
% ./result/bin/ihaskell-notebook --notebook-dir notebooks

but it (currently) doesn't use the on-disk versions of hvega and ihaskell-hvega. The notebooks/shell.nix file contains a version that uses Tweag I/O's jupyterWith environment environment but that unfortunately seems to be using "old" versions of IHaskell and ghc.

Testing

There is basic testing of the output of hvega, and the module also contains a tutorial which contains plots you can view; e.g. with Vega View or Vega-Desktop.

The notebooks/ directory contains a (very small, very random) sample of notebooks experimenting with hvega. I recommend using Tweag I/O's jupyterWith environment to view these (although I have not been able to get this to work with the circa 2023 changes to jupyterwith). At present there is support for Jupyter notebook, whereas the support for Jupyter lab is unfortunately limited (due to limitations on the current IHaskell environment and differences between the Jupyter Lab versions).

There is also a Data Haskell example notebook, and the Monad-Bayes blog series by tweag.io which starts here.

Development

I created this as a piece of procrastination, while procrastinating with a different task. At present I am not using it, due to lack of time. Please pop on over to GitHub, or ping me on Mastodon @[email protected] if you would like to help.