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170 lines
3.7 KiB
170 lines
3.7 KiB
# D3 Build
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## Lesson Objectives
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1. Add link to d3 library
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1. Add an `<svg>` tag and size it with D3
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1. Create some fake data for our app
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1. Add SVG circles and style them
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1. Create a linear scale
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## Add link to d3 library
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First thing we want to do is create basic `index.html` file:
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```html
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<!DOCTYPE html>
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<html>
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<head>
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<meta charset="utf-8">
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<title></title>
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</head>
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<body>
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</body>
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</html>
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```
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Now add a link to D3 at the bottom of your `<body>` tag in `index.html`:
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```html
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<body>
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<script src="https://d3js.org/d3.v4.min.js"></script>
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</body>
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```
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Now create `app.js`, which will store all of our code:
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```javascript
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console.log('this works');
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```
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and link to it in `index.html` at the bottom of the `<body>` tag:
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```html
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<body>
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<script src="https://d3js.org/d3.v4.min.js"></script>
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<script src="app.js" charset="utf-8"></script>
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</body>
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```
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## Add an `<svg>` tag and size it with D3
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At the top of the `<body>` tag in `index.html`, add an `<svg>` tag:
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```html
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<body>
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<svg></svg>
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<script src="https://d3js.org/d3.v4.min.js"></script>
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<script src="app.js" charset="utf-8"></script>
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</body>
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```
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In `app.js` create variables to hold the width and height of the `<svg>` tag:
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```javascript
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var WIDTH = 800;
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var HEIGHT = 600;
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```
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Next, we can use `d3.select()` to select a single element, in this case, the `<svg>` element:
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```javascript
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var WIDTH = 800;
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var HEIGHT = 600;
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d3.select('svg');
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```
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The return value of this is a d3 version of the element (just like jQuery), so we "chain" commands onto this. Let's add some styling to adjust the height/width of the element:
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```javascript
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d3.select('svg')
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.style('width', WIDTH)
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.style('height', HEIGHT);
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```
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## Create some fake data for our app
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In `app.js` let's create an array of "run" objects (**NOTE I'm storing the date as a string on purpose**):
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```javascript
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var WIDTH = 800;
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var HEIGHT = 600;
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var runs = [
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{
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id: 1,
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date: 'October 1, 2017 at 4:00PM',
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distance: 5.2
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},
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{
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id: 2,
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date: 'October 2, 2017 at 5:00PM',
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distance: 7.0725
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},
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{
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id: 3,
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date: 'October 3, 2017 at 6:00PM',
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distance: 8.7
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}
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];
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```
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## Add SVG circles and style them
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Add three circles to your `<svg>` element (each one will represent a run):
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```html
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<svg>
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<circle/>
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<circle/>
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<circle/>
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</svg>
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```
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Create `app.css` with some styling for the circles and our `svg` element:
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```css
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circle {
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r:5;
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fill: black;
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}
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svg {
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border: 1px solid black;
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}
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```
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and link to it in `index.html`
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```html
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<head>
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<meta charset="utf-8">
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<title></title>
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<link rel="stylesheet" href="app.css">
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</head>
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```
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## Create a linear scale
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- One of the most important things that D3 does is provide the ability to map points in the "domain" of data to points in the visual "range" using what's called a `scale`.
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- There are lots of different kinds of scales, but for now we're just going to use a `linear` scale which will map numeric data values to numeric visual values.
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In `app.js`:
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```javascript
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d3.select('svg')
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.style('width', WIDTH)
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.style('height', HEIGHT);
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var yScale = d3.scaleLinear(); //create the scale
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yScale.range([HEIGHT, 0]); //set the visual range (e.g. 600 to 0)
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yScale.domain([0, 10]); //set the data domain (e.g. 0 to 10)
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console.log(yScale(5)); //get a visual point from a data value
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console.log(yScale.invert(450)); //get a data values from a visual point
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```
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- Here we're saying that a data point of 0 to map to a visual height value of 600
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- This is because the lower the distance run (data value), the more we want to move the visual point down the Y axis
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- remember that the Y axis starts at 0 at the top and increases in value
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