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<!doctype html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>Vega, Vega-Lite & Altair</title>
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<div class="reveal">
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<div class="slides">
<section>
<h1>Vega, Vega-Lite & Altair</h1>
<h3>OH MY!</h3>
<p>
<h4></h4>
</p>
</section>
<section id="outline" class="level1">
<h1>Outline</h1>
<ul>
<li>Vega</li>
<li>Vega-Lite</li>
<li>Altair</li>
<li>Other ecosystem things</li>
<li>Opinions</li>
</ul>
</section>
<section id="grammar-of-graphics" class="level1">
<h1>Grammar of Graphics</h1>
<p>Declarative data visualizations</p>
<ul>
<li>how do you map properties of data to visual aesthetics?</li>
<li>focus on the guts of the problem over implementation details</li>
<li>very successful: influenced ggplot2, d3, etc</li>
</ul>
</section>
<section id="vega" class="level1">
<h1>Vega</h1>
<p>Grammar of Graphics as a data specification</p>
<ul>
<li>declarative to the max</li>
<li>built on (compiles to) d3.js</li>
<li>extremely powerful/configurable</li>
<li>interactive features, dataflow, etc</li>
<li>not suitable for day to day visualization tasks by itself (lots of boilerplate)</li>
<li>great compile-to target</li>
</ul>
</section>
<section id="example-vega" class="level1">
<h1>Example Vega</h1>
<pre><code>{"$schema":"https://vega.github.io/schema/vega/v3.0.json",
"autosize":"pad",
"padding":5,
"width":200,
"height":200,
"style":"cell",
"data":[{"name":"source_0","url":"https://vega.github.io/editor/data/cars.json",
"format":{"type":"json","parse":{"Horsepower":"number","Miles_per_Gallon":"number"}},
"transform":[{"type":"filter","expr":"datum[\"Horsepower\"] !== null && !isNaN(datum[\"Horsepower\"]) && datum[\"Miles_per_Gallon\"] !== null && !isNaN(datum[\"Miles_per_Gallon\"])"}]}],
"marks":[{"name":"marks",
"type":"symbol",
"style":["point"],
"from":{"data":"source_0"},
"encode":{"update": {"opacity":{"value":0.7},"fill":{"value":"transparent"},"stroke":{"scale":"color","field":"Origin"},"x":{"scale":"x","field":"Horsepower"},"y":{"scale":"y","field":"Miles_per_Gallon"}}}}],
"scales":[{"name":"x","type":"linear","domain":{"data":"source_0","field":"Horsepower"},"range":[0,{"signal":"width"}],"nice":true,"zero":true},
{"name":"y","type":"linear","domain":{"data":"source_0","field":"Miles_per_Gallon"},"range":[{"signal":"height"},0],"nice":true,"zero":true},
{"name":"color","type":"ordinal","domain":{"data":"source_0","field":"Origin","sort":true},"range":"category"}],
"axes":[{"scale":"x","orient":"bottom","title":"Horsepower","labelFlush":true,"labelOverlap":true,"tickCount":{"signal":"ceil(width/40)"},"zindex":1},
{"scale":"x","orient":"bottom","grid":true,"tickCount":{"signal":"ceil(width/40)"},"gridScale":"y","domain":false,"labels":false,"maxExtent":0,"minExtent":0,"ticks":false,"zindex":0},
{"scale":"y","orient":"left","title":"Miles_per_Gallon","labelOverlap":true,"tickCount":{"signal":"ceil(height/40)"},"zindex":1},{"scale":"y","orient":"left","grid":true,"tickCount":{"signal":"ceil(height/40)"},"gridScale":"x","domain":false,"labels":false,"maxExtent":0,"minExtent":0,"ticks":false,"zindex":0}],
"legends":[{"stroke":"color","title":"Origin","encode":{"symbols":{"update":{"opacity":{"value":0.7}}}}}],
"config":{"axisY":{"minExtent":30}}}</code></pre>
</section>
<section id="vega-lite" class="level1">
<h1>Vega-Lite</h1>
<p>Higher-level manifestation of Vega for day to day viz</p>
<ul>
<li>both restricts and extends vega with focus on productivity over control (do more with less)</li>
<li>compiles to Vega</li>
<li>Vega with sane defaults (style guide?)</li>
<li>early Vega-Lite was a bit limited, but v2 is phenomenally composable</li>
</ul>
</section>
<section id="example-vega-lite" class="level1">
<h1>Example Vega-Lite</h1>
<div class="sourceCode"><pre class="sourceCode json"><code class="sourceCode json"><span class="fu">{</span><span class="dt">"data"</span><span class="fu">:</span> <span class="fu">{</span><span class="dt">"url"</span><span class="fu">:</span> <span class="st">"https://vega.github.io/editor/data/cars.json"</span><span class="fu">},</span>
<span class="dt">"mark"</span><span class="fu">:</span> <span class="st">"point"</span><span class="fu">,</span>
<span class="dt">"encoding"</span><span class="fu">:</span> <span class="fu">{</span><span class="dt">"x"</span><span class="fu">:</span> <span class="fu">{</span><span class="dt">"field"</span><span class="fu">:</span> <span class="st">"Horsepower"</span><span class="fu">},</span>
<span class="dt">"y"</span><span class="fu">:</span> <span class="fu">{</span><span class="dt">"field"</span><span class="fu">:</span> <span class="st">"Miles_per_Gallon"</span><span class="fu">},</span>
<span class="dt">"color"</span><span class="fu">:</span> <span class="fu">{</span><span class="dt">"field"</span><span class="fu">:</span> <span class="st">"Origin"</span><span class="fu">}}}</span></code></pre></div>
</section>
<section id="json-ftw" class="level1">
<h1>JSON FTW</h1>
<p>Vega and Vega-Lite are just data</p>
<ul>
<li>can be created from any language with a natural interpretation of JSON (dictionaries, lists, numbers, strings, boolean)</li>
<li>can be easily passed between programs or written to disk</li>
<li>synergy!</li>
</ul>
</section>
<section id="server-side-rendering" class="level1">
<h1>Server side rendering</h1>
<p>The only way to compile Vega-Lite or Vega to SVG/PNG is with JS</p>
<ul>
<li>fine if you are targeting the browser (see <a href="https://github.com/vega/vega-embed">vega-embed</a>)</li>
<li>for generating SVG/PNG programatically, need a node (“server-side JS”) environment</li>
</ul>
<p>Thankfully SciComp has set some modules up for us to use this</p>
<div class="sourceCode"><pre class="sourceCode bash"><code class="sourceCode bash"><span class="ex">ml</span> nodejs-bundle</code></pre></div>
</section>
<section id="basic-cli-usage" class="level1">
<h1>Basic CLI usage</h1>
<p>Installing the vega/vega-lite node modules (and deps) gives you the following executables</p>
<div class="sourceCode"><pre class="sourceCode bash"><code class="sourceCode bash"><span class="ex">vl2svg</span> carviz.json
<span class="ex">vl2png</span> carviz.json
<span class="ex">vl2vg</span> carviz.json</code></pre></div>
</section>
<section id="altair" class="level1">
<h1>Altair</h1>
<p>OOP Python wrapper around Vega-Lite</p>
<ul>
<li>validation against Vega-Lite specs, for help debugging</li>
<li>adds constructors and conventions for improving concision, by obscuring some of vega-lite (pros/cons)</li>
<li>requires python3 and pandas; (me: kicking and screaming)</li>
</ul>
<pre><code>ml Python/3.6.4-foss-2016b-fh2</code></pre>
</section>
<section id="altair-example" class="level1">
<h1>Altair example</h1>
<div class="sourceCode"><pre class="sourceCode python"><code class="sourceCode python"><span class="im">import</span> altair <span class="im">as</span> alt
<span class="im">from</span> vega_datasets <span class="im">import</span> data
<span class="co"># data must be a data frame; for convenience, here the vega_datasets data</span>
data <span class="op">=</span> data.cars()
<span class="co"># Set mark type and encodings</span>
c <span class="op">=</span> alt.Chart(data).mark_point().encode(
x<span class="op">=</span><span class="st">'Horsepower:Q'</span>,
y<span class="op">=</span><span class="st">'Miles_per_Gallon:Q'</span>,
color<span class="op">=</span><span class="st">'Origin:N'</span>)</code></pre></div>
</section>
<section id="altair-to-vega-lite" class="level1">
<h1>Altair to Vega-Lite</h1>
<div class="sourceCode"><pre class="sourceCode python"><code class="sourceCode python"><span class="co"># ↓ This is all Altair really is...</span>
c.to_dict()
{<span class="st">'$schema'</span>: <span class="st">'https://vega.github.io/schema/vega-lite/v2.json'</span>,
<span class="st">'data'</span>: {<span class="st">'values'</span>: ...},
<span class="st">'config'</span>: {<span class="st">'view'</span>: {<span class="st">'height'</span>: <span class="dv">300</span>, <span class="st">'width'</span>: <span class="dv">400</span>}},
<span class="st">'mark'</span>: <span class="st">'point'</span>,
<span class="st">'encoding'</span>: {<span class="st">'color'</span>: {<span class="st">'field'</span>: <span class="st">'Origin'</span>, <span class="st">'type'</span>: <span class="st">'nominal'</span>},
<span class="st">'x'</span>: {<span class="st">'field'</span>: <span class="st">'Horsepower'</span>,
<span class="st">'type'</span>: <span class="st">'quantitative'</span>},
<span class="st">'y'</span>: {<span class="st">'field'</span>: <span class="st">'Miles_per_Gallon'</span>,
<span class="st">'type'</span>: <span class="st">'quantitative'</span>}}}</code></pre></div>
</section>
<section id="vega-lite-to-altair" class="level1">
<h1>Vega-Lite to Altair</h1>
<p>You can also do this</p>
<pre><code>import json
# Import from vega
with open("carviz.json") as json_handle:
vl_data = json.load(json_handle.read())
c = alt.from_dict(vl_data)</code></pre>
</section>
<section id="things-i-dont-like-about-altair" class="level1">
<h1>Things I don’t like about Altair</h1>
<ul>
<li>py3k</li>
<li>pandas</li>
<li>weird indentation</li>
<li>obfuscates data model, challenging more intricate setups</li>
<li>no vega</li>
</ul>
</section>
<section id="server-side-without-altair" class="level1">
<h1>Server side without altair</h1>
<pre><code>import subprocess, json
c = {'data': ...,
'mark': ...,
'encoding': ...}
with open('my-vega-lite.json', 'w') as json_handle:
json.dump(c, json_handle)
subprocess.call(['vl2svg', 'my-vega-lite.json', 'rendered.svg'])</code></pre>
<p>I’ll probably release a snappy library with helpers along these lines…</p>
</section>
<section id="other-ecosystem-things" class="level1">
<h1>Other ecosystem things</h1>
<ul>
<li><a href="http://vega.github.io/polestar/">polestar</a> - Tableau like browser tool based on vega-lite
<ul>
<li>exports as json</li>
</ul></li>
<li><a href="https://vega.github.io/editor/">vega-editor</a> - Live renders Vega/Vega-Lite code as you type
<ul>
<li>enables gist-based sharing/editing/colaboration</li>
</ul></li>
<li>more examples of <a href="https://vega.github.io/vega/examples/">Vega</a> and <a href="https://vega.github.io/vega-lite/examples/">Vega-Lite</a></li>
<li><a href="https://github.com/Zsailer/phylovega">phylovega</a> - vega-lite for phylogenetic trees!?</li>
</ul>
</section>
</div>
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