Intermediate D3

Objectives

  • Use D3 to calculate extreme values in a data set

  • Use D3 to scale data

  • Build scatterplots using D3 and SVG

  • Use D3 to add axes and gridlines to graphs

  • Add axis labels and titles to graphs

  • Build histograms using D3 and SVG

  • Build pie charts using D3 and SVG

Extrema and Scales

Problems Last Time

  • Finding extreme values manually
  • Scaling our data manually

Code Example

Code: http://bit.ly/2tzBwFC

Live Site: http://bit.ly/2uTHcKT

Extreme Values

d3.max(dataArr [, callback])

How to associate values to array elements

d3.min(dataArr [, callback])

Scales

d3.scaleLinear()

.domain([num1, num2])

.range([num3, num4])

Scales

example

1

17

-4

52

5

9

24

10

Scatter Plots

Code Example

Code: http://bit.ly/2vTC8TY​

Live Site: http://bit.ly/2w9NG4E

Scatter Plot Visualization

Life Expectancy

Births per Capita

d3.extent(dataArr [, callback])

calculates min an max, returns them in an array!

var people = [
  { name: "Brett", age: 40 }, 
  { name: "Mackenzie", age: 30 }, 
  { name: "Arya", age: 78 }, 
  { name: "Lee", age: 22 }
];

d3.extent(people, function(d) { return d.age; }); 
// [ 22, 78 ]

Extreme Values

Axes and Gridlines

Code Example

Code: http://bit.ly/2wa3JzE

Live Site: http://bit.ly/2tMPGzi

Axes

50

40

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20

10

0

60

70

80

90

100

Axes

d3.axisBottom(scale)

d3.axisLeft(scale)

d3.axisRight(scale)

d3.axisTop(scale)

Gridlines

axis.tickSize([size])

Set a new tick size

Ticks stretch in the direction of the axis

(e.g. left for axisLeft)

Gridlines

axis.tickSizeOuter([size])

Set a new tick size just for the outer ticks

Histograms

(Part 1)

Histograms

98, 53, 62, 70, 82, 38, 72, 52, 76, 58, 62, 19, 34, 54, 81, 34, 8, 91, 38, 61, 60, 5, 20, 16, 81

50

40

30

20

10

0

60

70

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90

100

Code Example

Code: http://bit.ly/2wvwnzg

Generating a Histogram

d3.histogram()

  • Returns a function
  • The returned function creates bins for data passed into it

Generating a Histogram

histogram.value([value])

Specifies what value should be used when creating bins

Generating a Histogram

histogram.domain([domain])

Specifies the domain of values (i.e. the min and max) for the histogram generator

Histograms Continued

Code Example

Code: http://bit.ly/2vcN0M2​

Live Site: http://bit.ly/2wwyzqq

Generating a Histogram

histogram.thresholds([value])

  • Specifies how the histogram generator should separate your data into bins
  • If value is an array, the thresholds will be based on the elements in the array
  • If value is a number, D3 will try to make that many bins (but no guarantees!)
num # of bins num # of bins
1 1 11 12
2 2 12 12
3 2 13 12
4 5 14 12
5 5 15 12
6 5 16 12
7 5 17 12
8 5 18 12
9 12 19 25
10 12 20 25

Thresholds Example

Scales Revisited

scale.ticks([count])

  • Returns approximately count intermediate values from the scale's domain
  • You are not guaranteed to get exactly count values!

YOUR

TURN

Pie Charts

Pie Charts

Arcs and SVG

<path d="M-222.94,-200.73,300,0,0,1,0,-300L0,0Z" 
      fill="rgb(26, 188, 156)">
</path>
<path d="M-259.80,150A300,300,0,0,1,-222.94,-200.73L0,0Z" 
      fill="rgb(236, 240, 241)"></path>
<path d="M0,-300A300,300,0,0,1,176.33,242.70L0,0Z" 
      fill="rgb(241, 196, 15)">
</path>
<path d="M176.33,242.70A300,300,0,0,1,-259.80,150L0,0Z" 
      fill="rgb(155, 89, 182)">
</path>

Code Example

Code: http://bit.ly/2weZpQV

Live Site: http://bit.ly/2izEcxW

Scales Revisited

d3.scaleOrdinal()

Maps a discrete set of points (e.g. [1, 2, 3]) to another discrete set of points (e.g. ['a','b','c'])

Centering SVG

SVG

Transformed g element

pie chart

pie chart

Pie Chart Helpers

{ 
  region: "Chile", 
  continent: "SA", 
  year: 1967, 
  births: 259729
}
"M1.7757378587636622e-14,-290
A290,290,0,1,1,-285.4954404332191,-50.91515974483682
L-147.67005539649264,-26.335427454225943
A150,150,0,1,0,9.184850993605149e-15,-150
Z"

Pie Chart Helpers

d3.pie()

  • Returns a function
  • The returned function transforms data
  • Like d3.histogram, has a value method

Angle Measurements

2π

360°

Pie Chart Helpers

d3.arc()

Converts JavaScript objects into path commands

Arc Helpers

  • arc.innerRadius([val]) - set the inner radius
  • arc.outerRadius([val]) - set the outer radius
  • arc.startAngle([val]) - set the start angle
  • arc.endAngle([val]) - set the end angle

Examples

Pie Charts Continued

Code Example

Code: http://bit.ly/2vzgFhz

Live Site: http://bit.ly/2vswiYQ

Chart Styling Helpers

Examples

  • pie.padAngle - set padding between arcs
  • arc.padAngle - set padding between arcs
  • arc.cornerRadius - round arc corners

Sorting Arcs

pie.sort([comparator])

  • comparator(a, b) < 0: a should come before b
  • comparator(a, b) > 0: a should come after b
  • comparator(a, b) == 0: a and b are equivalent

YOUR

TURN