Data visualizations in Clojure and ClojureScript using Vega and Vega-lite
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Great and powerful data vizualizationz


Oz is a library for data-driven, REPL-based data visualization in the browser, using vega and vega-lite.

Oz itself is almost no code. The real magic is in vega & vega-lite.

If you don't already know about vega/vega-lite, it's worth taking a few minutes to orient yourself with this mindblowing talk/demo from the creators at the Interactive Data Lab (IDL) at University of Washington.

Vega & Vega-Lite talk from IDL

The long story short is that vega and vega-lite are declarative grammars for describing data visualizations. Of note, they are based on the Grammar of Graphics, which served as the guiding light for the popular R ggplot2 viz library. In this setting, we define visualizations by specifying at a high level how attributes of our data map to aesthetics properties of visualization. Vega-lite in particular aims to be a less verbose and more automated flavor of vega, with features focused on maximal leverage for day to day usage.

Watched the IDL talk and hungry for more content? Here's another which focuses on the philosophical ideas behind Vega & Vega-Lite, how they relate to Clojure, and how you can use the tools from Clojure using Oz.

Seajure Clojure + Vega/Vega-Lite talk

About oz specifically...

Oz itself provides:

  • a REPL API for for pushing vega and vega-lite data to a browser window over websockets
  • client side vega and vega-lite Reagent components
  • an API for composing vega & vega-lite together in the context of html as hiccup for document and dashboard generation
  • plot publishing/sharing features via GitHub gists and the IDL's live vega editor

It also has the following eventual goals:

  • use as a static build tool for publishing scientific documents
  • provide an API for combining vega and vega-lite into a single plot (vega for detailed control, vega-lite for the simple bits)
  • higher level viz constructors, as they accrete and become useful


Some other things in the Vega/Vega-Lite ecosystem you may want to look at

  • Hanami - Really cool library from Jon Anthony with high level constructors for Vega/Vega-Lite data
  • Vega Editor - Wonderful editing tool (as mentioned above) for editing and sharing Vega/Vega-Lite data visualizations.
  • Voyager - Also from the IDL, Voyager is a wonderful Tableau like (drag and drop) tool for exploring data and constructing exportable Vega/Vega-Lite visualizations.
  • Vega Examples - A
  • Vega home - More great stuff from the IDL folks

REPL Usage

Add oz to your leiningen project dependencies

Clojars Project

To get things going, require oz and start the plot server as follows:

(require '[oz.core :as oz])


This will fire up a browser window with a websocket connection for funneling view data back and forth.

Next we'll define a function for generating some dummy data

(defn group-data [& names]
  (apply concat (for [n names]
  (map-indexed (fn [i x] {:x i :y x :col n}) (take 20 (repeatedly #(rand-int 100)))))))


The simplest function for displaying vega or vega-lite is oz/v!. It will display a single vega or vega-lite plot in any connected browser windows.

For example, a simple line plot:

  (def line-plot
    {:data {:values (group-data "monkey" "slipper" "broom")}
     :encoding {:x {:field "x"}
                :y {:field "y"}
                :color {:field "col" :type "nominal"}}
     :mark "line"})

  ;; Render the plot to the 
  (oz/v! line-plot)

Should render something like:

lines plot

Another example:

(def stacked-bar
  {:data {:values (group-data "munchkin" "witch" "dog" "lion" "tiger" "bear")}
   :mark "bar"
   :encoding {:x {:field "x"
                  :type "ordinal"}
              :y {:aggregate "sum"
                  :field "y"
                  :type "quantitative"}
              :color {:field "col"
                      :type "nominal"}}})

(oz/v! stacked-bar)

This should render something like:

bars plot

vega support

For vega instead of vega-lite, you can also specify :mode :vega to oz/v!:

;; load some example vega (this may only work from within a checkout of oz; haven't checked)

(require '[cheshire.core :as json])

(def vega-data (json/parse-string (slurp ( "example-cars-plot.vega.json")))) 
(oz/v! vega-data :mode :vega)

This should render like:

cars plot


This is a more powerful function which will let you compose vega and vega-lite views together with other html, using hiccup notation. The idea is to provide some quick and dirty utilities for building composite view dashboards, and for the construction of documents.

For demonstration we'll combine the three plots above into one:

(oz/view! [:div
           [:h1 "Look ye and behold"]
           [:p "A couple of small charts"]
           [:div {:style {:display "flex" :flex-direction "row"}}
            [:vega-lite line-plot]
            [:vega vega-data]]
           [:p "A wider, more expansive chart"]
           [:vega-lite stacked-bar]
           [:h2 "If ever, oh ever a viz there was, the vizard of oz is one because, because, because..."]
           [:p "Because of the wonderful things it does"]])

Note that the vega and vega-lite specs are described in the output vega as using the :vega and :vega-lite keys.

You should now see something like this:

composite view

Note that vega-lite already has very powerful and impressive plot concatenation features, and that in general these should be preferred as they allow for tighter coupling of the data and interactive features of vega-lite. But again, when doing something quick and dirty, this functionality may prove useful.

Also note that while not illustrated above, you can specify multiple maps in these vectors, and they will be merged into one. So for example, you can do [:vega-lite stacked-bar {:width 100}] to override the width.

Sharing features

Looking to share your cool plots with someone? We've got you covered.

user=> (oz/publish-plot! line-plot)
Gist url:
Vega editor url:

This will post the plot content to a GitHub Gist, and use the gist uuid to create a vega-editor link which prints to the screen. When you visit the vega-editor link, it will load the gist in question and place the content in the editor. It renders the plot, and updates in real time as you tinker with the code, making it a wonderful yet simple tool for sharing and prototyping.


As client side reagent components

If you like, you may also use the Reagent components found at oz.core to render vega and/or vega-lite you construct client side.

 [oz.core/vega { ... }]
 [oz.core/vega-lite { ... }]]

At present, these components do not take a second argument. The merging of spec maps described above applies prior to application of this reagent component.

Local development

For development environment, dev/utils.clj has


Then do yer thing.

Debugging & updating Vega/Vega-Lite versions

I'm frequently shocked (pleasantly) at how if I find I'm unable to do something in Vega or Vega-Lite that I think I should, updating the Vega or Vega-Lite version fixes the problem. As a side note, I think this speaks volumes of the stellar job (pun intended) the IDL has been doing of developing these tools. More to the point though, if you find yourself unable to do something you expect to be able to do, it's not a bad idea to try

  1. Make sure your Oz version is up to date, in case there's a more recent Vega/Vega-Lite versions required there fix the problem.
  2. Check cljsjs to see if there's a more recent version of the Vega/Vega-Lite (or Vega-Embed or Vega-Hover, as appropriate). You can override whatever version of these libraries is getting used by Oz by adding the correspoding [cljsjs/vega-* ...] coordinates to your project.clj dependencies list. As long as this comes before your Oz version specification, your cljsjs version specification should take precedence.
  3. If there's not a more recent version on cljsjs, but there are more up to date versions of the JS libraries (check the github pages or npm). Read below for instructions.
  4. If this still doesn't solve your problem, file an issue on the appropriate Vega GitHub project. I've found the developers super responsive to issues.

Updating cljsjs packages

For more context and information, see the cljsjs creating pacakages, updating packages and creating externs documentation. For convenience, I've automated much of this work in the script at ./bin/

Building and deploying oz

This is mostly for my convenience....



Copyright © 2018 Christopher Small

Forked from Vizard (with thanks) - Copyright © 2017 Yieldbot, Inc.

Distributed under the Eclipse Public License either version 1.0 or (at your option) any later version.