78 lines
3.1 KiB
Markdown
78 lines
3.1 KiB
Markdown
---
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id: 587d7fac367417b2b2512bdb
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title: Set a Domain and a Range on a Scale
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challengeType: 6
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---
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## Description
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<section id='description'>
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By default, scales use the identity relationship - the input value maps to the output value. But scales can be much more flexible and interesting.
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Say a data set has values ranging from 50 to 480. This is the input information for a scale, and is also known as the domain.
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You want to map those points along the <code>x</code> axis on the SVG canvas, between 10 units and 500 units. This is the output information, which is also known as the range.
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The <code>domain()</code> and <code>range()</code> methods set these values for the scale. Both methods take an array of at least two elements as an argument. Here's an example:
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<blockquote>// Set a domain<br>// The domain covers the set of input values<br>scale.domain([50, 480]);<br>// Set a range<br>// The range covers the set of output values<br>scale.range([10, 500]);<br>scale(50) // Returns 10<br>scale(480) // Returns 500<br>scale(325) // Returns 323.37<br>scale(750) // Returns 807.67<br>d3.scaleLinear()</blockquote>
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Notice that the scale uses the linear relationship between the domain and range values to figure out what the output should be for a given number. The minimum value in the domain (50) maps to the minimum value (10) in the range.
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</section>
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## Instructions
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<section id='instructions'>
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Create a scale and set its domain to <code>[250, 500]</code> and range to <code>[10, 150]</code>.
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<strong>Note</strong><br>You can chain the <code>domain()</code> and <code>range()</code> methods onto the <code>scale</code> variable.
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</section>
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## Tests
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<section id='tests'>
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```yml
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tests:
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- text: Your code should use the <code>domain()</code> method.
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testString: assert(code.match(/\.domain/g), 'Your code should use the <code>domain()</code> method.');
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- text: The <code>domain()</code> of the scale should be set to <code>[250, 500]</code>.
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testString: assert(JSON.stringify(scale.domain()) == JSON.stringify([250, 500]), 'The <code>domain()</code> of the scale should be set to <code>[250, 500]</code>.');
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- text: Your code should use the <code>range()</code> method.
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testString: assert(code.match(/\.range/g), 'Your code should use the <code>range()</code> method.');
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- text: The <code>range()</code> of the scale should be set to <code>[10, 150]</code>.
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testString: assert(JSON.stringify(scale.range()) == JSON.stringify([10, 150]), 'The <code>range()</code> of the scale should be set to <code>[10, 150]</code>.');
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- text: The text in the <code>h2</code> should be -102.
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testString: assert($('h2').text() == '-102', 'The text in the <code>h2</code> should be -102.');
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```
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</section>
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## Challenge Seed
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<section id='challengeSeed'>
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<div id='html-seed'>
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```html
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<body>
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<script>
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// Add your code below this line
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const scale = d3.scaleLinear();
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// Add your code above this line
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const output = scale(50);
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d3.select("body")
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.append("h2")
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.text(output);
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</script>
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</body>
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```
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</div>
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</section>
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## Solution
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<section id='solution'>
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```js
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// solution required
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```
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</section>
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