102 lines
5.0 KiB
Markdown
102 lines
5.0 KiB
Markdown
|
---
|
||
|
id: 587d7fa9367417b2b2512bce
|
||
|
title: Dynamically Set the Coordinates for Each Bar
|
||
|
required:
|
||
|
- src: 'https://cdnjs.cloudflare.com/ajax/libs/d3/4.3.0/d3.min.js'
|
||
|
challengeType: 6
|
||
|
---
|
||
|
|
||
|
## Description
|
||
|
<section id='description'>
|
||
|
The last challenge created and appended a rectangle to the <code>svg</code> element for each point in <code>dataset</code> to represent a bar. Unfortunately, they were all stacked on top of each other.
|
||
|
The placement of a rectangle is handled by the <code>x</code> and <code>y</code> attributes. They tell D3 where to start drawing the shape in the <code>svg</code> area. The last challenge set them each to 0, so every bar was placed in the upper-left corner.
|
||
|
For a bar chart, all of the bars should sit on the same vertical level, which means the <code>y</code> value stays the same (at 0) for all bars. The <code>x</code> value, however, needs to change as you add new bars. Remember that larger <code>x</code> values push items farther to the right. As you go through the array elements in <code>dataset</code>, the x value should increase.
|
||
|
The <code>attr()</code> method in D3 accepts a callback function to dynamically set that attribute. The callback function takes two arguments, one for the data point itself (usually <code>d</code>) and one for the index of the data point in the array. The second argument for the index is optional. Here's the format:
|
||
|
<blockquote>selection.attr("property", (d, i) => {<br> /* <br> * d is the data point value<br> * i is the index of the data point in the array<br> */<br>})</blockquote>
|
||
|
It's important to note that you do NOT need to write a <code>for</code> loop or use <code>forEach()</code> to iterate over the items in the data set. Recall that the <code>data()</code> method parses the data set, and any method that's chained after <code>data()</code> is run once for each item in the data set.
|
||
|
</section>
|
||
|
|
||
|
## Instructions
|
||
|
<section id='instructions'>
|
||
|
Change the <code>x</code> attribute callback function so it returns the index times 30.
|
||
|
<strong>Note</strong><br>Each bar has a width of 25, so increasing each <code>x</code> value by 30 adds some space between the bars. Any value greater than 25 would work in this example.
|
||
|
</section>
|
||
|
|
||
|
## Tests
|
||
|
<section id='tests'>
|
||
|
|
||
|
```yml
|
||
|
tests:
|
||
|
- text: The first <code>rect</code> should have an <code>x</code> value of 0.
|
||
|
testString: 'assert($(''rect'').eq(0).attr(''x'') == ''0'', ''The first <code>rect</code> should have an <code>x</code> value of 0.'');'
|
||
|
- text: The second <code>rect</code> should have an <code>x</code> value of 30.
|
||
|
testString: 'assert($(''rect'').eq(1).attr(''x'') == ''30'', ''The second <code>rect</code> should have an <code>x</code> value of 30.'');'
|
||
|
- text: The third <code>rect</code> should have an <code>x</code> value of 60.
|
||
|
testString: 'assert($(''rect'').eq(2).attr(''x'') == ''60'', ''The third <code>rect</code> should have an <code>x</code> value of 60.'');'
|
||
|
- text: The fourth <code>rect</code> should have an <code>x</code> value of 90.
|
||
|
testString: 'assert($(''rect'').eq(3).attr(''x'') == ''90'', ''The fourth <code>rect</code> should have an <code>x</code> value of 90.'');'
|
||
|
- text: The fifth <code>rect</code> should have an <code>x</code> value of 120.
|
||
|
testString: 'assert($(''rect'').eq(4).attr(''x'') == ''120'', ''The fifth <code>rect</code> should have an <code>x</code> value of 120.'');'
|
||
|
- text: The sixth <code>rect</code> should have an <code>x</code> value of 150.
|
||
|
testString: 'assert($(''rect'').eq(5).attr(''x'') == ''150'', ''The sixth <code>rect</code> should have an <code>x</code> value of 150.'');'
|
||
|
- text: The seventh <code>rect</code> should have an <code>x</code> value of 180.
|
||
|
testString: 'assert($(''rect'').eq(6).attr(''x'') == ''180'', ''The seventh <code>rect</code> should have an <code>x</code> value of 180.'');'
|
||
|
- text: The eighth <code>rect</code> should have an <code>x</code> value of 210.
|
||
|
testString: 'assert($(''rect'').eq(7).attr(''x'') == ''210'', ''The eighth <code>rect</code> should have an <code>x</code> value of 210.'');'
|
||
|
- text: The ninth <code>rect</code> should have an <code>x</code> value of 240.
|
||
|
testString: 'assert($(''rect'').eq(8).attr(''x'') == ''240'', ''The ninth <code>rect</code> should have an <code>x</code> value of 240.'');'
|
||
|
|
||
|
```
|
||
|
|
||
|
</section>
|
||
|
|
||
|
## Challenge Seed
|
||
|
<section id='challengeSeed'>
|
||
|
|
||
|
<div id='html-seed'>
|
||
|
|
||
|
```html
|
||
|
<body>
|
||
|
<script>
|
||
|
const dataset = [12, 31, 22, 17, 25, 18, 29, 14, 9];
|
||
|
|
||
|
const w = 500;
|
||
|
const h = 100;
|
||
|
|
||
|
const svg = d3.select("body")
|
||
|
.append("svg")
|
||
|
.attr("width", w)
|
||
|
.attr("height", h);
|
||
|
|
||
|
svg.selectAll("rect")
|
||
|
.data(dataset)
|
||
|
.enter()
|
||
|
.append("rect")
|
||
|
.attr("x", (d, i) => {
|
||
|
// Add your code below this line
|
||
|
|
||
|
|
||
|
|
||
|
// Add your code above this line
|
||
|
})
|
||
|
.attr("y", 0)
|
||
|
.attr("width", 25)
|
||
|
.attr("height", 100);
|
||
|
</script>
|
||
|
</body>
|
||
|
```
|
||
|
|
||
|
</div>
|
||
|
|
||
|
|
||
|
|
||
|
</section>
|
||
|
|
||
|
## Solution
|
||
|
<section id='solution'>
|
||
|
|
||
|
```js
|
||
|
// solution required
|
||
|
```
|
||
|
</section>
|