Teach Yourself D3.js

D3 is a JavaScript framework used for data visualization.
Learning how to work with D3.js is very easy. If you begin with the basics, you’ll see how easy it is to use D3, because:

  • the DOM function names are much shorter than those in the legacy DOM library.
  • the same functions are used for both setting and getting values.
  • setters return a value, so you can keep working with the same element without repeating its name.

If you already know some framework, you probably feel that there’s nothing new under the sun, which is good because it makes learning the new stuff easier.

So, What’s New?

In D3, you can:
* add and remove SVG and HTML elements using the setters and getter.
* set and get the element’s properties, attributes, styles, text and… data

Getting Started

First, download the framework from http://d3js.org
After you include it in your script, you can use selections, that is wrappers for elements.
To get a selection, use one of the functions:

  • d3.select(selector) – to select the first element matching selector.
  • d3.selectAll(selector) – to select the all elements matching selector.

Like the d3 object, selections has their select and selectAll methods to select descendant.

If selection is a selection, it’s easy to understand what selection.text(), selection.attribute(), selection.style(), selection.insert(), and selection.append() do. But, what does selection.data() do?

Data And Update Selection

The selection’s method data() helps you use the HTML DOM as a database.
selection.data() returns an array of all data that belongs to the elements of the selectionץ The data is held in the property __data__ of the element.
selection.data(arr, func) – defines an update selection and distribute the elements of array arr to the elements of selection.
func(d,i)is a function that:

  • receives d an element of arr and its index i.
  • returns a record key.

If func is not passed, the key is the element’s index.

A recommended way to create an update selection is:
var updSelection = selection1.selectAll(selector).data(arr)

Now, updSelection is a selection of existing elements whose data has been changed.
In addition, updSelection has to methods:

  • updSelection.enter() – returns place holders for elements to be created under selection1.
  • updSelection.exit()– returns elements that have lost their data, and are usually to be removed.

Using the data

The methods attr, style, property, text and data can accept a function as a value to set. The function will be called for each element of the selection’s data. And its arguments will be the array element and its index.

Now, let us see it in an example.
The following code arranges data in a donut layout::

<!DOCTYPE html>
<html>
<head>
<meta http-equiv="Content-type" content="text/html; charset=utf-8">
<title>Testing Pie Chart</title>
<script type="text/javascript" src="d3.min.js"></script>

<style type="text/css">
.slice text {
font-size: 12pt;
font-family: Arial;
}
</style>
</head>
<body>
<script type="text/javascript">
var width = 300, 
    height = 300, 
    radius = 100, 
    color = d3.scale.category20c(); //builtin range of colors


// Step 1: creating a container for the donut chart, and attach raw data to it.
var vis = d3.select("body")
            .append("svg")     //create the SVG element inside the <body>
            .datum([{"label":"first", "value":20},
                    {"label":"second", "value":10},
                    {"label":"third", "value":30},
                    {"label":"fourth", "value":25}])       
            .attr({"width": width, "height": height})  
            .append("g")
            .attr("transform", "translate(" + radius + "," + radius + ")") //move the center of the pie chart from 0, 0 to r, r



// Step two: defining the accessors of the layour function. 
//           The function 'pie' will use the 'value' accessor to compute the arc's length.
var pie = d3.layout.pie() 
            .value(function(d) { return d.value; })
            .sort(function(a,b){return a.label<b.label?-1:a.label==b.label?0:1;});

// Step 3: Create the update selection. 
var updateSelection = vis.selectAll("g") 
                         .data(pie);    // This will use the function 'pie' to create arc data from the row data attached to the visualisation element.


// Step 4: Using the data in the update selection to create shape elements.
var arc = d3.svg.arc() 
            .outerRadius(radius)
            .innerRadius(radius / 2)
;
updateSelection.enter()
               .append('g')
               .attr('class','slice')
               .append("path")
               .style("fill", function(d, i) { return color(i); } ) //set the color for each slice to be chosen from the color function defined above
               .attr("d", arc);                                     // Create the arc from the arc data attached to each element.

updateSelection.append("text") 
               .attr("transform", 
                     function(d) { 
                       return "translate(" + arc.centroid(d) + ")"; 
                     })
               .attr("text-anchor", "middle")                  
               .text(function(d, i) { return d.data.label; }); 


</script>
</body>
</html> 

And following is the chart:
enter image description here

For more funcions, see the API Reference.

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StackEdit: Markdown Editor

Hello, World!

I am a blog post written in Markdown, and sent from the StackEdit editor.

Do you know those files with suffix ‘.md’? They are markdown documents, and they are easy to write and easy to read because they don’t have to contain HTML tags!

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Type “[The Example Site](http://example.com)” to get the following link:

The Example Site

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CSS Animations (Without Javascript)

CSS3 is the newest CSS standard, and is supported by all modern browsers. Among the new style properties supported in CSS3, there are animation properties. Those properties allows you to animate HTML elements without the need of Javascript. CSS3 allows more animation options than those done by the non-standard yet supported marquee tags. It also allows gradual changes of font sizes, colors, rotation angles, etc.

To make an element or a group of elements (defined by a selector) animated, add animation properties to its selector’s property block. For multi-browser support, writing each animation property twice – once with the prefix ‘-webkit-‘ and once without – is recommended.

In addition, you should add two animation rules: “@keyframes” and “@-webkit-keyframes” to describe the animated changes of elements.

NOTE: Chrome, Safari & Opera require the ‘-webkit-‘ prefix` Firefox and Explorer 10+ do not.

Animation Attributes

For my own convenience, please allow me to drop the ‘-webkit-‘ prefix from the following attribute names:

  • animation: animation-name duration;
  • animation-iteration-count: number-of-iterations;
    number-of-iterations may be an integer or “infinite”
  • animation-direction: direction.
    direction of change, not only left-to-right or top-to-bottom, but also, for example, from onecolor to another. the values for this property can be: normal, reverse, alternate, alternate-reverse, initial, or inherit,
  • animation-timing-function: function
    Function can be: linear, ease, cubic-bezier, etc. Read more here.

Here’s a little code example:

      div {
        position: relative;
        overflow: hidden;
        /* Chrome, Safari, Opera: with the prefix '-webkit-', others without. */
        -webkit-animation: myfirst 10s; 
        animation: myfirst 10s;
        -webkit-animation-iteration-count: infinite;
        animation-iteration-count: infinite;
        -webkit-animation-direction: normal;
        animation-direction: normal;
        -webkit-animation-timing-function: linear;
        animation-timing-function: linear;
      }

Read more about animation properties here.

Key Frame Rules

A key frame rule describes the gradually changed values at each key frame. The key frame value can be ‘from’, ‘to’ or the percentage of progress.

The syntax is:

@[-webkit-]keyframes animation-name {
   keyframe-value: {property-list}
   .
   .
   .
}

Here’s a little code example:

      /* Chrome, Safari, Opera */
        @-webkit-keyframes myfirst {
        from {color: red; font-size: 12px; left: 0px;}
        to {color: black; font-size: 48px; left: 100%; transform: rotate(-90deg)}

      }

      /* Standard syntax */
      @keyframes myfirst {
        from {color: red; font-size: 12px; left: 0px; }
        to {color: black; font-size: 48px; left: 100%; transform: rotate(-90deg);}
      } 

Read more about key frames here.