152 lines
3.9 KiB
Markdown
152 lines
3.9 KiB
Markdown
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---
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id: 587d7fa9367417b2b2512bce
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title: Dynamically Set the Coordinates for Each Bar
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challengeType: 6
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forumTopicId: 301487
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dashedName: dynamically-set-the-coordinates-for-each-bar
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---
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# --description--
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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.
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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.
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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.
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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:
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```js
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selection.attr("property", (d, i) => {
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})
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```
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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.
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# --instructions--
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Change the `x` attribute callback function so it returns the index times 30.
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**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.
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# --hints--
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The first `rect` should have an `x` value of `0`.
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```js
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assert($('rect').eq(0).attr('x') == '0');
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```
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The second `rect` should have an `x` value of `30`.
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```js
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assert($('rect').eq(1).attr('x') == '30');
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```
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The third `rect` should have an `x` value of `60`.
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```js
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assert($('rect').eq(2).attr('x') == '60');
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```
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The fourth `rect` should have an `x` value of `90`.
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```js
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assert($('rect').eq(3).attr('x') == '90');
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```
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The fifth `rect` should have an `x` value of `120`.
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```js
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assert($('rect').eq(4).attr('x') == '120');
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```
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The sixth `rect` should have an `x` value of `150`.
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```js
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assert($('rect').eq(5).attr('x') == '150');
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```
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The seventh `rect` should have an `x` value of `180`.
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```js
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assert($('rect').eq(6).attr('x') == '180');
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```
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The eighth `rect` should have an `x` value of `210`.
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```js
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assert($('rect').eq(7).attr('x') == '210');
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```
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The ninth `rect` should have an `x` value of `240`.
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```js
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assert($('rect').eq(8).attr('x') == '240');
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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 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) => {
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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("y", 0)
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.attr("width", 25)
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.attr("height", 100);
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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 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) => {
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return i * 30
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})
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.attr("y", 0)
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.attr("width", 25)
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.attr("height", 100);
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</script>
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</body>
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```
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