D3.js v4

Shirley Wu

(@sxywu)

Shirley Wu

(@sxywu)

 

independent creator of

data visualizations

 

1/2 data sketches

co-organizer d3.unconf

Agenda

D3 Ecosystem

 

Selections

Data binding

Enter-append

 

Scales

Shapes

 

Update & Exit

Transitions

 

Forces

d3 ecosystem

API Reference:

Selections

Scales & Axes

Shapes

Forces

 

Bl.ocks & Blockbuilder (search)

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)

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 & Axes

// get min/max
var min = d3.min(data, d => d[city]);
var max = d3.max(data, d => d[city]);

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

var yScale = d3.scaleLinear()
  .domain(extent)
  .range([height, 0]);
// continuous
d3.scaleLinear()
d3.scaleLog()
d3.scaleTime()

// ordinal
d3.scaleBand()

Scales I use often:

Scales & Axes

  var yAxis = d3.axisLeft()
    .scale(yScale); // pass in a scale

  d3.select('svg')
    // create a group element we can translate
    // so that the axis will be visible in SVG
    .append('g')
    .attr('transform', 'translate(40, 20)')
    // selection.call(yAxis) is the same as yAxis(selection)
    // and an axis will be created within the selection
    .call(yAxis);

Scales & Axes

Play with the code

(Play with different scales, try different tick values and formats)

Docs that may help:

Scales

Axes

Exercise time

Starter code

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 Elements

SVG Paths

SVG Transform

shapes

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L705.7534246575343,139.1489361702127L707.945205479452,163.40425531914894
L710.1369863013699,178.7234042553191L712.3287671232877,174.8936170212766
L714.5205479452055,160.85106382978722L716.7123287671233,145.53191489361697
L718.9041095890411,157.0212765957447L721.0958904109589,169.7872340425532
L723.2876712328766,135.31914893617017L725.4794520547946,112.34042553191489
L727.6712328767123,107.23404255319141L729.8630136986302,122.55319148936167
L732.054794520548,142.9787234042553L734.2465753424658,149.36170212765956
L736.4383561643835,145.53191489361697L738.6301369863014,178.7234042553191
L740.8219178082192,173.61702127659572L743.0136986301369,186.38297872340422
L745.2054794520548,160.85106382978722L747.3972602739726,137.87234042553192
L749.5890410958905,136.59574468085106L751.7808219178082,135.31914893617017
L753.9726027397261,136.59574468085106L756.1643835616438,149.36170212765956
L758.3561643835617,139.1489361702127L760.5479452054794,145.53191489361697
L762.7397260273972,163.40425531914894L764.931506849315,151.91489361702122
L767.1232876712328,163.40425531914894L769.3150684931508,181.27659574468083
L771.5068493150685,157.0212765957447L773.6986301369864,157.0212765957447
L775.8904109589041,131.48936170212764L778.082191780822,149.36170212765956
L780.2739726027397,144.25531914893617L782.4657534246575,142.9787234042553
L784.6575342465753,182.55319148936172L786.8493150684931,160.85106382978722
L789.0410958904109,176.17021276595747L791.2328767123288,172.34042553191486
L793.4246575342466,191.4893617021276L795.6164383561644,185.1063829787234
L797.8082191780823,168.51063829787233L800,153.19148936170208">

d3-shape calculates the path attribute so we don't have to

shapes

shapes

var data = [
  {date: new Date(2007, 3, 24), value: 93.24},
  {date: new Date(2007, 3, 25), value: 95.35},
  {date: new Date(2007, 3, 26), value: 98.84},
  {date: new Date(2007, 3, 27), value: 99.92},
  {date: new Date(2007, 3, 30), value: 99.80},
  {date: new Date(2007, 4,  1), value: 99.47},
  …
];

var line = d3.line()
  .x((d) => { return xScale(d.date); })
  .y((d) => { return yScale(d.value); });

d3.select('svg')
  .append('path')
  .attr('d', line(data));

d3.line()

Input: array of objects

 

Output: path that connects each point (object) with lines or curves

shapes

d3.pie()

var pie = d3.pie();

// input
var data = [1, 1, 2, 3, 5, 8, 13, 21];

pie(data);

// output
[
  {"data":  1, "value":  1, "startAngle": 6.050474740247008, "endAngle": 6.166830023713296, "padAngle": 0},
  {"data":  1, "value":  1, "startAngle": 6.166830023713296, "endAngle": 6.283185307179584, "padAngle": 0},
  {"data":  2, "value":  2, "startAngle": 5.817764173314431, "endAngle": 6.050474740247008, "padAngle": 0},
  {"data":  3, "value":  3, "startAngle": 5.468698322915565, "endAngle": 5.817764173314431, "padAngle": 0},
  {"data":  5, "value":  5, "startAngle": 4.886921905584122, "endAngle": 5.468698322915565, "padAngle": 0},
  {"data":  8, "value":  8, "startAngle": 3.956079637853813, "endAngle": 4.886921905584122, "padAngle": 0},
  {"data": 13, "value": 13, "startAngle": 2.443460952792061, "endAngle": 3.956079637853813, "padAngle": 0},
  {"data": 21, "value": 21, "startAngle": 0.000000000000000, "endAngle": 2.443460952792061, "padAngle": 0}
]
  var pie = {
    "data":  1, "value":  1,
    "startAngle": 6.050474740247008,
    "endAngle": 6.166830023713296,
  };

  var arc = d3.arc()
    .innerRadius(0)
    .outerRadius(100)
    .startAngle(d => d.startAngle)
    .endAngle(d => d.endAngle);

  arc(pie);
  // M-23.061587074244123,-97.30448705798236A100,100,0,0,1,-11.609291412523175,-99.32383577419428L0,0Z

d3.arc()

(Code)

exercise time

Docs that may help:

Shape

update & exit

Object constancy

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

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

Exercise time

Starter code

x: barley sites

y: yield value

animate across years

Forces

Understanding the Force

Forces

Starter code

Forces

Position (forceX, forceY)

Collision (forceCollide)

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