110 lines
2.6 KiB
Markdown
110 lines
2.6 KiB
Markdown
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---
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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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forumTopicId: 301491
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dashedName: set-a-domain-and-a-range-on-a-scale
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---
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# --description--
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By default, scales use the identity relationship. This means the input value maps to the output value. However, scales can be much more flexible and interesting.
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Say a dataset has values ranging from 50 to 480. This is the input information for a scale, also known as the <dfn>domain</dfn>.
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You want to map those points along the `x` axis on the SVG canvas, between 10 units and 500 units. This is the output information, also known as the <dfn>range</dfn>.
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The `domain()` and `range()` 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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```js
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// Set a domain
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// The domain covers the set of input values
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scale.domain([50, 480]);
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// Set a range
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// The range covers the set of output values
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scale.range([10, 500]);
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scale(50) // Returns 10
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scale(480) // Returns 500
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scale(325) // Returns 323.37
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scale(750) // Returns 807.67
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d3.scaleLinear()
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```
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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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# --instructions--
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Create a scale and set its domain to `[250, 500]` and range to `[10, 150]`.
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**Note**
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You can chain the `domain()` and `range()` methods onto the `scale` variable.
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# --hints--
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Your code should use the `domain()` method.
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```js
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assert(code.match(/\.domain/g));
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```
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The `domain()` of the scale should be set to `[250, 500]`.
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```js
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assert(JSON.stringify(scale.domain()) == JSON.stringify([250, 500]));
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```
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Your code should use the `range()` method.
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```js
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assert(code.match(/\.range/g));
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```
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The `range()` of the scale should be set to `[10, 150]`.
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```js
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assert(JSON.stringify(scale.range()) == JSON.stringify([10, 150]));
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```
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The text in the `h2` should be -102.
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```js
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assert($('h2').text() == '-102');
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```
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# --seed--
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## --seed-contents--
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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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# --solutions--
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```html
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<body>
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<script>
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const scale = d3.scaleLinear();
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scale.domain([250, 500])
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scale.range([10, 150])
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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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