D3: Data Driven Documents

 

Overview

Building blocks of charts

D3 overview

Appending elements, binding data

Example chart

Building blocks of charts

What elements constitute a chart?

What elements constitute a chart?

All you have to do is learn how to arrange these elements into charts

Building blocks of charts

<!-- Container Div -->
<div>
	<!-- Container svg for visual elements -->
	<svg>
		<!-- Rectangle element -->
		<rect x=10 y=10 height=20 width=100></rect>
	</svg>
</div>		

Visual elements are part of the DOM

Elements are wrapped in a Scalable Vector Graphic (SVG)

Limitations

Tedious

Not scalable

Not flexible

Not dynamic

D3 Overview

What is D3?

A JavaScript library that makes charts

Not a charting library

DOM manipulation library

Binds data to visual elements

Easily included in HTML

<script src="http://d3js.org/d3.v3.min.js"></script>

So what can D3 do?

All you have to do is learn how to arrange these elements into charts

 

(and D3 can help!)

Appending elements to the page

Appending elements

Select element

d3.select('#my-div')

Append an element to your selection

d3.select('#my-div').append('svg')

Assign attributes and styles

d3.select('#my-div').append('svg')
	.attr('width', 100)
	.attr('height', 100)
	.style('border', '1px solid black')

Binding data

Entering, exiting

Binding data

mySvg.selectAll('circle')
    .data([1,2,3]) // binds data to selection

Enter elements

mySvg.selectAll('circle')
    .data([1,2,3])
    .enter() // returns elements in data not on page

Exit elements

mySvg.selectAll('circle')
    .data([1,2,3])
    .exit() // returns elements on page not in data

Using .call()

Write a function to do your positioning

var circleFunc = function(circle) {
    circle.attr('r', 15)
          .attr('fill', 'blue')
          .attr('x', function(d) {d * 50})
          .attr('class', 'shape')
}

Pass elements to your positioning function

var circles = d3.selectAll('circle').data(myData)

circles.enter().append('circle')
      .call(circleFunc) 
      // Passes each circle to your function

Generalizing

var draw = function(data) {
    // Bind data you pass in
    var circles = svg.selectAll('circle').data(data)
	
    // Enter new elements
    circles.enter().append('circle').call(circleFunc)
	
    // Exit elements that may have left
    circles.exit().remove()
	
    // Transition all circles to new position
    svg.selectAll('circle').transition()
        .duration(1500).call(circleFunc)  
}

Scales

Translate from an input domain to an output range

var scale = d3.scale.linear()
                 .domain([0,10])
                 .range([0, 100])

scale(5) // returns 50

Use built in d3.min and d3.max functions

d3.min([1,2,3]) // returns 1
var data = [{x:1, y:1},{x:2, y:2},{x:3, y:5}]
d3.max(data, function(d) {return d.y}) // returns 5

Example application

Scatterplot exercise

Fork my repo

Clone in desktop

Start your local server

cd "d3-demo"
python -m SimpleHTTPServer 8080

Assignments

Project proposals (due before next class)

d3

By Michael Freeman

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