156 lines
3.9 KiB
Markdown
156 lines
3.9 KiB
Markdown
|
---
|
||
|
|
id: 587d7fa9367417b2b2512bce
|
||
|
|
title: Dynamically Set the Coordinates for Each Bar
|
||
|
|
challengeType: 6
|
||
|
|
forumTopicId: 301487
|
||
|
|
dashedName: dynamically-set-the-coordinates-for-each-bar
|
||
|
|
---
|
||
|
|
|
||
|
|
# --description--
|
||
|
|
|
||
|
|
The last challenge created and appended a rectangle to the `svg` element for each point in `dataset` to represent a bar. Unfortunately, they were all stacked on top of each other.
|
||
|
|
|
||
|
|
The placement of a rectangle is handled by the `x` and `y` attributes. They tell D3 where to start drawing the shape in the `svg` 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 `y` value stays the same (at 0) for all bars. The `x` value, however, needs to change as you add new bars. Remember that larger `x` values push items farther to the right. As you go through the array elements in `dataset`, the x value should increase.
|
||
|
|
|
||
|
|
The `attr()` 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 `d`) and one for the index of the data point in the array. The second argument for the index is optional. Here's the format:
|
||
|
|
|
||
|
|
```js
|
||
|
|
selection.attr("property", (d, i) => {
|
||
|
|
/*
|
||
|
|
* d is the data point value
|
||
|
|
* i is the index of the data point in the array
|
||
|
|
*/
|
||
|
|
})
|
||
|
|
```
|
||
|
|
|
||
|
|
It's important to note that you do NOT need to write a `for` loop or use `forEach()` to iterate over the items in the data set. Recall that the `data()` method parses the data set, and any method that's chained after `data()` is run once for each item in the data set.
|
||
|
|
|
||
|
|
# --instructions--
|
||
|
|
|
||
|
|
Change the `x` attribute callback function so it returns the index times 30.
|
||
|
|
|
||
|
|
**Note**
|
||
|
|
Each bar has a width of 25, so increasing each `x` value by 30 adds some space between the bars. Any value greater than 25 would work in this example.
|
||
|
|
|
||
|
|
# --hints--
|
||
|
|
|
||
|
|
The first `rect` should have an `x` value of 0.
|
||
|
|
|
||
|
|
```js
|
||
|
|
assert($('rect').eq(0).attr('x') == '0');
|
||
|
|
```
|
||
|
|
|
||
|
|
The second `rect` should have an `x` value of 30.
|
||
|
|
|
||
|
|
```js
|
||
|
|
assert($('rect').eq(1).attr('x') == '30');
|
||
|
|
```
|
||
|
|
|
||
|
|
The third `rect` should have an `x` value of 60.
|
||
|
|
|
||
|
|
```js
|
||
|
|
assert($('rect').eq(2).attr('x') == '60');
|
||
|
|
```
|
||
|
|
|
||
|
|
The fourth `rect` should have an `x` value of 90.
|
||
|
|
|
||
|
|
```js
|
||
|
|
assert($('rect').eq(3).attr('x') == '90');
|
||
|
|
```
|
||
|
|
|
||
|
|
The fifth `rect` should have an `x` value of 120.
|
||
|
|
|
||
|
|
```js
|
||
|
|
assert($('rect').eq(4).attr('x') == '120');
|
||
|
|
```
|
||
|
|
|
||
|
|
The sixth `rect` should have an `x` value of 150.
|
||
|
|
|
||
|
|
```js
|
||
|
|
assert($('rect').eq(5).attr('x') == '150');
|
||
|
|
```
|
||
|
|
|
||
|
|
The seventh `rect` should have an `x` value of 180.
|
||
|
|
|
||
|
|
```js
|
||
|
|
assert($('rect').eq(6).attr('x') == '180');
|
||
|
|
```
|
||
|
|
|
||
|
|
The eighth `rect` should have an `x` value of 210.
|
||
|
|
|
||
|
|
```js
|
||
|
|
assert($('rect').eq(7).attr('x') == '210');
|
||
|
|
```
|
||
|
|
|
||
|
|
The ninth `rect` should have an `x` value of 240.
|
||
|
|
|
||
|
|
```js
|
||
|
|
assert($('rect').eq(8).attr('x') == '240');
|
||
|
|
```
|
||
|
|
|
||
|
|
# --seed--
|
||
|
|
|
||
|
|
## --seed-contents--
|
||
|
|
|
||
|
|
```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>
|
||
|
|
```
|
||
|
|
|
||
|
|
# --solutions--
|
||
|
|
|
||
|
|
```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) => {
|
||
|
|
return i * 30
|
||
|
|
})
|
||
|
|
.attr("y", 0)
|
||
|
|
.attr("width", 25)
|
||
|
|
.attr("height", 100);
|
||
|
|
</script>
|
||
|
|
</body>
|
||
|
|
```
|