91 lines
2.5 KiB
Markdown
91 lines
2.5 KiB
Markdown
---
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id: 587d7fac367417b2b2512bdc
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title: >-
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Use the d3.max and d3.min Functions to Find Minimum and Maximum Values in a Dataset
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challengeType: 6
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forumTopicId: 301496
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dashedName: >-
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use-the-d3-max-and-d3-min-functions-to-find-minimum-and-maximum-values-in-a-dataset
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---
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# --description--
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The D3 methods `domain()` and `range()` set that information for your scale based on the data. There are a couple methods to make that easier.
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Often when you set the domain, you'll want to use the minimum and maximum values within the data set. Trying to find these values manually, especially in a large data set, may cause errors.
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D3 has two methods - `min()` and `max()` to return this information. Here's an example:
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```js
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const exampleData = [34, 234, 73, 90, 6, 52];
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d3.min(exampleData)
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d3.max(exampleData)
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```
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A dataset may have nested arrays, like the `[x, y]` coordinate pairs that were in the scatter plot example. In that case, you need to tell D3 how to calculate the maximum and minimum. Fortunately, both the `min()` and `max()` methods take a callback function. In this example, the callback function's argument `d` is for the current inner array. The callback needs to return the element from the inner array (the `x` or `y` value) over which you want to compute the maximum or minimum. Here's an example for how to find the min and max values with an array of arrays:
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```js
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const locationData = [[1, 7],[6, 3],[8, 3]];
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const minX = d3.min(locationData, (d) => d[0]);
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```
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`minX` would have the value `1`.
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# --instructions--
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The `positionData` array holds sub arrays of x, y, and z coordinates. Use a D3 method to find the maximum value of the z coordinate (the third value) from the arrays and save it in the `output` variable.
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# --hints--
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The text in the `h2` should be `8`.
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```js
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assert(output == 8 && $('h2').text() == '8');
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```
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Your code should use the `max()` method.
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```js
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assert(
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code.match(/\.max/g),
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'Your code should use the <code>max()</code> method.'
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);
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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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const positionData = [[1, 7, -4],[6, 3, 8],[2, 9, 3]]
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// Add your code below this line
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const output = undefined; // Change this line
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// Add your code above this line
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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 positionData = [[1, 7, -4],[6, 3, 8],[2, 9, 3]]
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const output = d3.max(positionData, (d) => d[2])
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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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