Data Visualization workshop

Shirley Wu

(@sxywu)

You will learn:

SVG Paths

SVG Transforms

 

Selections

Data binding

Enter-append

 

Scales

 

Update & Exit

Transitions

 

Nesting elements

SVG Elements

rect
x: x-coordinate of top-left
y: y-coordinate of top-left
width
height

circle
cx: x-coordinate of center
cy: y-coordinate of center
r: radius

text
x: x-coordinate
y: y-coordinate
dx: x-coordinate offset
dy: y-coordinate offset
text-anchor: horizontal text alignment

Hi!

path
d: path to follow

Moveto, Lineto, Curveto, Arcto

SVG Paths

SVG Transforms

Exercise time

Create 3 unique petal shapes

Starter code

Selection & Data

  <svg>
    <rect />
    <rect />
    <rect />
    <rect />
    <rect />
  </svg>
  <script>
    var data = [100, 250, 175, 200, 120];
    
    d3.selectAll('rect')
    	.data(data)
    	.attr('x', (d, i) => i * rectWidth)
    	.attr('y', d => height - d)
    	.attr('width', rectWidth)
    	.attr('height', d => d)
    	.attr('fill', 'blue')
    	.attr('stroke', '#fff');

  </script>

Selection & Data

5 rectangle elements

Select all rectangle elements that exist

  <svg>
    <rect />
    <rect />
    <rect />
    <rect />
    <rect />
  </svg>
  <script>
    var data = [100, 250, 175, 200, 120];
    
    d3.selectAll('rect')
    	.data(data)
    	.attr('x', (d, i) => i * rectWidth)
    	.attr('y', d => height - d)
    	.attr('width', rectWidth)
    	.attr('height', d => d)
    	.attr('fill', 'blue')
    	.attr('stroke', '#fff');

  </script>

"Bind" data to the selections

Selection & Data

  <svg>
    <rect />
    <rect />
    <rect />
    <rect />
    <rect />
  </svg>
  <script>
    var data = [100, 250, 175, 200, 120];
    
    d3.selectAll('rect')
    	.data(data)
    	.attr('x', (d, i) => i * rectWidth)
    	.attr('y', d => height - d)
    	.attr('width', rectWidth)
    	.attr('height', d => d)
    	.attr('fill', 'blue')
    	.attr('stroke', '#fff');

  </script>

Loop through each rectangle selection

Get passed in (data, index)

Selection & Data

  <svg>
    <rect />
    <rect />
    <rect />
    <rect />
    <rect />
  </svg>
  <script>
    var data = [100, 250, 175, 200, 120];
    
    d3.selectAll('rect')
    	.data(data)
    	.attr('x', (d, i) => i * rectWidth)
    	.attr('y', d => height - d)
    	.attr('width', rectWidth)
    	.attr('height', d => d)
    	.attr('fill', 'blue')
    	.attr('stroke', '#fff');

  </script>

Selection & Data

Play with the code

(Change some numbers, add/remove a rect, console log all the things)

Enter-append

  <svg></svg>
  <script>
    var rectWidth = 100;
    var height = 300;
    var data = [100, 250, 175, 200, 120];
    
    var svg = d3.select('svg');
    svg.selectAll('rect')
    	.data(data)
    	.enter().append('rect')
    	.attr('x', (d, i) => i * rectWidth)
    	.attr('y', d => height - d)
    	.attr('width', rectWidth)
    	.attr('height', d => d)
    	.attr('fill', 'blue')
    	.attr('stroke', '#fff');

  </script>

Wut, no rectangle elements?!

So what are we even selecting?

A: an empty selection

So how are those bars appearing?

Enter-append

  <svg></svg>
  <script>
    var rectWidth = 100;
    var height = 300;
    var data = [100, 250, 175, 200, 120];
    
    var svg = d3.select('svg');
    svg.selectAll('rect')
    	.data(data)
    	.enter().append('rect')
    	.attr('x', (d, i) => i * rectWidth)
    	.attr('y', d => height - d)
    	.attr('width', rectWidth)
    	.attr('height', d => d)
    	.attr('fill', 'blue')
    	.attr('stroke', '#fff');

  </script>

Magic ✨

Enter-append

  <svg></svg>
  <script>
    var rectWidth = 100;
    var height = 300;
    var data = [100, 250, 175, 200, 120];
    
    var svg = d3.select('svg');
    svg.selectAll('rect')
    	.data(data)
    	.enter().append('rect')
    	.attr('x', (d, i) => i * rectWidth)
    	.attr('y', d => height - d)
    	.attr('width', rectWidth)
    	.attr('height', d => d)
    	.attr('fill', 'blue')
    	.attr('stroke', '#fff');

  </script>

Enter-append

Play with the code

(Try adding/removing some numbers, and make sure to console log all the things)

let's make a flower

  1. Get data ready, and use the first movie data
  2. Create 6 petals using previously created paths
  3. Translate and rotate the petals

 

Starter code

Complete code

Scales & Axes

  d3.scaleLinear()
    .domain([min, max]) // input
    .range([min, max]); // output

scale: mapping from

data attributes (domain)

to display (range)

 

 

date → x-value

value → y-value

value → opacity

etc.

Scales

// get min/max
var height = 600;
var data = [
    {date: new Date('01-01-2015'), temp: 0},
    {date: new Date('01-01-2017'), temp: 3}
];

var min = d3.min(data, d => d.date);
var max = d3.max(data, d => d.date);

// or use extent, which gives back [min, max]
var extent = d3.extent(data, d => d.date);

var yScale = d3.scaleLinear()
  .domain([min, max])
  .range([height, 0]);

Scales

// continuous
d3.scaleLinear()
d3.scaleLog()
d3.scaleTime()

// ordinal
d3.scaleBand()

Scales I use often:

Let's make a flower

Type of petal: parental guidance rating

Size of flower: IMDb rating out of 10

Number of petals: number of IMDb votes

 

  1. Create scale (scaleLinear and scaleQuantize)
  2. Get data ready, and use the first movie data
  3. Create number of petals based on data
  4. Rotate and scale petals

 

Starter code

Complete code

Hint: use SVG transform's translate, rotate, and scale (in that order)

update & exit

update & exit

  // bars includes update selection
  var bars = svg.selectAll('rect')
    .data(data, d => d);

  // exit
  bars.exit().remove();

  // enter
  var enter = bars.enter().append('rect')
    .attr('width', rectWidth)
    .attr('stroke', '#fff');

  // enter + update
  bars = enter.merge(bars)
    .attr('x', (d, i) => i * rectWidth)
    .attr('y', d => height - d)
    .attr('height', d => d)
    .attr('fill', d => colors(d));

key function: controls which datum is assigned to which element

update & exit

  // bars includes update selection
  var bars = svg.selectAll('rect')
    .data(data, d => d);

  // exit
  bars.exit().remove();

  // enter
  var enter = bars.enter().append('rect')
    .attr('width', rectWidth)
    .attr('stroke', '#fff');

  // enter + update
  bars = enter.merge(bars)
    .attr('x', (d, i) => i * rectWidth)
    .attr('y', d => height - d)
    .attr('height', d => d)
    .attr('fill', d => colors(d));

Enter selection: chain attributes that don't depend on data

Combines 2 selections into one

Enter+update selection: chain attrs dependent on data

Exit selection

Play with the code

Update-exit

Let's update the flowers!

At every second, draw the next flower.

 

  1. Create function, within function:
  2. Calculate petal data for specific movie
  3. Bind data and draw flower with enter-update-exit pattern

 

Starter code

Complete code

Transitions

Emphasize changes in state

(object constancy)

Transitions

var t = d3.transition()
  .duration(1000);
var svg = d3.select('svg');
   
var bars = svg.selectAll('rect')
  .data(data, d => d);

// exit
bars.exit().transition(t)
  .attr('y', height)
  .attr('height', 0)
  .remove();

// enter
var enter = bars.enter().append('rect')
  .attr('width', rectWidth)
  .attr('stroke', '#fff')
  .attr('y', height);
// enter + update
bars = enter.merge(bars)
  .attr('x', (d, i) => i * rectWidth)
  .attr('fill', d => colors(d))
  .transition(t)
  .attr('y', d => height - d)
  .attr('height', d => d);

Define transition, syncs animation everywhere it's used

Animate height down to 0 before removing

Animate remaining <rect>'s height to their next state

Transitions

var t = d3.transition()
  .duration(1000);
var svg = d3.select('svg');
   
var bars = svg.selectAll('rect')
  .data(data, d => d);

// exit
bars.exit().transition(t)
  .attr('y', height)
  .attr('height', 0)
  .remove();

// enter
var enter = bars.enter().append('rect')
  .attr('width', rectWidth)
  .attr('stroke', '#fff')
  .attr('y', height);
// enter + update
bars = enter.merge(bars)
  .attr('x', (d, i) => i * rectWidth)
  .attr('fill', d => colors(d))
  .transition(t)
  .attr('y', d => height - d)
  .attr('height', d => d);

go from state A to state B

Everything after .transition(): state B to transition to

Same attributes set before .transition(): state A to transition from

If attributes not specified for A, d3 extrapolates from default

Transitions

Play with the code

nesting elements

Nest elements when you want to apply the same styles and transforms to a group of elements

<g> element that consist of petals and leaves, has translate and scale applied

<path> element for each petal with rotate applied

nesting elements

const data = [
  {fill: 'red', circle: [2, 25, 50]},
  {fill: 'blue', circle: [10, 100, 150]},
];

const svg = d3.select("body").append("svg")
  .attr("width", 960)
  .attr("height", 500)

const groups = svg.selectAll('g')
  .data(data).enter().append('g')
  .attr('fill', d => d.fill)
  .attr('transform', 'translate(10,10)');

const circles = groups.selectAll('circle')
  .data(d => d.circle).enter().append('circle')
  .attr('cx', d => d)
  .attr('r', 10);

nesting elements

const data = [
  {fill: 'red', circle: [2, 25, 50]},
  {fill: 'blue', circle: [10, 100, 150]},
];

const svg = d3.select("body").append("svg")
  .attr("width", 960)
  .attr("height", 500)

const groups = svg.selectAll('g')
  .data(data).enter().append('g')
  .attr('fill', d => d.fill)
  .attr('transform', 'translate(10,10)');

const circles = groups.selectAll('circle')
  .data(d => d.circle).enter().append('circle')
  .attr('cx', d => d)
  .attr('r', 10);

Use <g> element to nest child elements *in SVG, only <g> elements can have children

nesting elements

const data = [
  {fill: 'red', circle: [2, 25, 50]},
  {fill: 'blue', circle: [10, 100, 150]},
];

const svg = d3.select("body").append("svg")
  .attr("width", 960)
  .attr("height", 500)

const groups = svg.selectAll('g')
  .data(data).enter().append('g')
  .attr('fill', d => d.fill)
  .attr('transform', 'translate(10,10)');

const circles = groups.selectAll('circle')
  .data(d => d.circle).enter().append('circle')
  .attr('cx', d => d)
  .attr('r', 10);
const data = [
  {fill: 'red', circle: [2, 25, 50]},
  {fill: 'blue', circle: [10, 100, 150]},
];

const svg = d3.select("body").append("svg")
  .attr("width", 960)
  .attr("height", 500)

const groups = svg.selectAll('g')
  .data(data).enter().append('g')
  .attr('fill', d => d.fill)
  .attr('transform', 'translate(10,10)');

const circles = groups.selectAll('circle')
  .data(d => d.circle).enter().append('circle')
  .attr('cx', d => d)
  .attr('r', 10);

nesting elements

const data = [
  {fill: 'red', circle: [2, 25, 50]},
  {fill: 'blue', circle: [10, 100, 150]},
];

const svg = d3.select("body").append("svg")
  .attr("width", 960)
  .attr("height", 500)

const groups = svg.selectAll('g')
  .data(data).enter().append('g')
  .attr('fill', d => d.fill)
  .attr('transform', 'translate(10,10)');

const circles = groups.selectAll('circle')
  .data(d => d.circle).enter().append('circle')
  .attr('cx', d => d)
  .attr('r', 10);

nesting elements

Play with the code

Nesting elements

Let's make all the flowers!

Full-day creative data visualization workshop

By Shirley Wu

Full-day creative data visualization workshop

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