101 lines
4.7 KiB
Markdown
101 lines
4.7 KiB
Markdown
---
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id: 587d7fa9367417b2b2512bd0
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title: Invert SVG Elements
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required:
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- src: 'https://cdnjs.cloudflare.com/ajax/libs/d3/4.3.0/d3.min.js'
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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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You may have noticed the bar chart looked like it's upside-down, or inverted. This is because of how SVG uses (x, y) coordinates.
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In SVG, the origin point for the coordinates is in the upper-left corner. An <code>x</code> coordinate of 0 places a shape on the left edge of the SVG area. A <code>y</code> coordinate of 0 places a shape on the top edge of the SVG area. Higher <code>x</code> values push the rectangle to the right. Higher <code>y</code> values push the rectangle down.
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To make the bars right-side-up, you need to change the way the <code>y</code> coordinate is calculated. It needs to account for both the height of the bar and the total height of the SVG area.
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The height of the SVG area is 100. If you have a data point of 0 in the set, you would want the bar to start at the bottom of the SVG area (not the top). To do this, the <code>y</code> coordinate needs a value of 100. If the data point value were 1, you would start with a <code>y</code> coordinate of 100 to set the bar at the bottom. Then you need to account for the height of the bar of 1, so the final <code>y</code> coordinate would be 99.
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The <code>y</code> coordinate that is <code>y = heightOfSVG - heightOfBar</code> would place the bars right-side-up.
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</section>
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## Instructions
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<section id='instructions'>
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Change the callback function for the <code>y</code> attribute to set the bars right-side-up. Remember that the <code>height</code> of the bar is 3 times the data value <code>d</code>.
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<strong>Note</strong><br>In general, the relationship is <code>y = h - m * d</code>, where <code>m</code> is the constant that scales the data points.
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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: The first <code>rect</code> should have a <code>y</code> value of 64.
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testString: 'assert($("rect").eq(0).attr("y") == h - (dataset[0] * 3), "The first <code>rect</code> should have a <code>y</code> value of 64.");'
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- text: The second <code>rect</code> should have a <code>y</code> value of 7.
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testString: 'assert($("rect").eq(1).attr("y") == h - (dataset[1] * 3), "The second <code>rect</code> should have a <code>y</code> value of 7.");'
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- text: The third <code>rect</code> should have a <code>y</code> value of 34.
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testString: 'assert($("rect").eq(2).attr("y") == h - (dataset[2] * 3), "The third <code>rect</code> should have a <code>y</code> value of 34.");'
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- text: The fourth <code>rect</code> should have a <code>y</code> value of 49.
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testString: 'assert($("rect").eq(3).attr("y") == h - (dataset[3] * 3), "The fourth <code>rect</code> should have a <code>y</code> value of 49.");'
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- text: The fifth <code>rect</code> should have a <code>y</code> value of 25.
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testString: 'assert($("rect").eq(4).attr("y") == h - (dataset[4] * 3), "The fifth <code>rect</code> should have a <code>y</code> value of 25.");'
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- text: The sixth <code>rect</code> should have a <code>y</code> value of 46.
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testString: 'assert($("rect").eq(5).attr("y") == h - (dataset[5] * 3), "The sixth <code>rect</code> should have a <code>y</code> value of 46.");'
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- text: The seventh <code>rect</code> should have a <code>y</code> value of 13.
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testString: 'assert($("rect").eq(6).attr("y") == h - (dataset[6] * 3), "The seventh <code>rect</code> should have a <code>y</code> value of 13.");'
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- text: The eighth <code>rect</code> should have a <code>y</code> value of 58.
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testString: 'assert($("rect").eq(7).attr("y") == h - (dataset[7] * 3), "The eighth <code>rect</code> should have a <code>y</code> value of 58.");'
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- text: The ninth <code>rect</code> should have a <code>y</code> value of 73.
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testString: 'assert($("rect").eq(8).attr("y") == h - (dataset[8] * 3), "The ninth <code>rect</code> should have a <code>y</code> value of 73.");'
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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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const dataset = [12, 31, 22, 17, 25, 18, 29, 14, 9];
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const w = 500;
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const h = 100;
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const svg = d3.select("body")
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.append("svg")
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.attr("width", w)
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.attr("height", h);
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svg.selectAll("rect")
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.data(dataset)
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.enter()
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.append("rect")
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.attr("x", (d, i) => i * 30)
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.attr("y", (d, i) => {
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// Add your code below this line
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// Add your code above this line
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})
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.attr("width", 25)
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.attr("height", (d, i) => 3 * d);
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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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