Extension:Graph/en

The Graph extension allows a tag to describe data visualizations such as bar charts, pie charts, timelines, and histograms (demo) in a JSON format that renders a Vega-based graph.

General info
Graph extension allows powerful Vega based graphs to be added to the wiki pages. Graphs can be interactive.

The easiest way to add a graph is to use a ready-made template such as. These templates hide all Vega complexities. Power users can use the Graph Sandbox to develop graphs. Graph sandbox allows wiki template syntax in addition to JSON. The extension integrates with VisualEditor, providing a simple tool/wizard which generates basic graphs, by entering values directly to the editor.

Useful links

 * Vega 2 documentation - restored Vega 2 documentation pages on nyurik/vega/wiki.
 * - General recommendations on how to use graphs in wiki.
 * - step by step instructions how to build a complex interactive graph from scratch
 * - for many samples and usage tricks.
 * TechTalk Video - a WMF tech talk discussing the Graph extension, including a great demo of the Lyra editor (also installed on labs).
 * You may also be interested in some of the Vega future capabilities (Keynote by Jeffrey Heer).
 * Vega for devs - best place of all Vega resources
 * Video introduction into interactive Vega
 * Video introduction into interactive Vega

Additional config setup
If you are looking to replicate a production environment like en.wiki you will need to complete the following steps:


 * Install, and , and enable SVG uploads
 * If you use vagrant, you can use
 * Import mediawiki.org's Module:Graph, Module:Graph/doc, and Template:Nowrap/styles.css (export link)
 * Import enwiki's Module:Chart and Module:Chart/Default colors (export link)
 * Import the file File:Circle_frame.svg

Debugging graphs (GraphSandbox)
A sandbox is provided at Special:GraphSandbox that works similar to the Vega graph editor. The MediaWiki tool includes compatibility code that maps older Vega schemas to the currently enabled version. Inserting an old schema in the main text area will print a modified and modernized schema underneath the graph where possible.

Charts examples
See for many samples and usage tricks.

User defined fallback
When using client side rendering, it is possible to use Wikimedia Commons to provide a static fallback image to  users. This is a temporary solution until a new service is put in place to provide server side rendering.

The user must first upload the static graph to Wikimedia Commons.

Fallback images have two variables  and.

relates to a Wikimedia Commons filename.

is the fallback images width in pixels.

These variables are pass through the graph in the following way:

Where lua modules are used such as Module:Graph then these variables can be provided via the tag function. If were adapted, it would look like this:

It would then be utilised in a template in the following manner:

If a fallbackWidth isn't provided but an image is defined then the extension will derive the width from the provided graph width. The reason for this is there is frequently a difference in the rendered image width and the actual image width.

External data
HTTP(S) protocol cannot be used to get data for the graph. Instead, use one of the custom wiki protocols like,  , and others.

Graph extension uses the  setting to control how these protocols are resolved: Note that because queries rely on the structure of wikibase items, they may suddenly stop working if the underlying data is edited and changes, as it may yield incomplete, empty or invalid data that can't be used to create a graph. In these cases the graph will end up empty (see T168601).

Internals
When parsing, the Graph extension expands all template parameters/expressions, and stores the complete graph definitions in the ParserOutput, using graph hashes for IDs.

The graph extension adds HTML to the page where graphs should go, a with a graph-id as the attribute. Sample:

The Graph extension adds an  ResourceLoader JavaScript module to the page that includes the Vega library, and puts the JSON of graph definitions into a JavaScript   variable named. Once the client has loaded this module, the Vega JavaScript library populates each with an HTML canvas and draws the graph in it, replacing the static image.

Security features
can be configured to disallow referencing untrusted data sources (e.g. Wikimedia only allows data from the Wikimedia sites).

License
Vega library is distributed under a modified BSD license acceptable under for us to use.

This appears to be a copy of the BSD license, with some minor (acceptable) modifications. It's not a problem for us to use it, although ideally they would not make changes like this to the license. It's better if people do not make these changes to their license, to avoid confusion (like this) about whether the license is safe for open-source use.

wgGraphAllowedDomains
See the section on external data.

VisualEditor module
Since summer 2015, the Graph extension also comes with a module (ext.graph.VisualEditor) which enables graph editing within VisualEditor.

This module was a result of a Google Summer of Code 2015 project. See T89287 for more details.

This module allows users to see graphs within VisualEditor, as opposed to alien extension nodes. Furthermore, users can open up a dialog to edit a graph's type, data and padding. The UI also offers a way to edit a graph's raw JSON specification within VE without having to switch to the classic wikitext editor, in case more advanced users want to tweak settings not supported by the UI.

This first step serves as a stepping stone for many possibilities with graph editing within VisualEditor, and there are a lot of ways in which the module can be improved and expanded.

Troubleshooting broken graphs
Errors with graphs will be logged in the developer console.

Error: Bad constructor arguments (T277906)
To fix: Replace filepath:Earthmap1000x500compac.jpg with filepath:Earthmap1000x500.jpg

Example.

TypeError: undefined is not an object (evaluating 'datum.firstYear.value')
To fix: Make sure you have not set default as null

Example.