[D3] 7. Quantitative Scales

# Quantitative Scales

    var colorScale = d3.scale.quantile()

            .domain([d3.max(dataset) / 4, d3.max(dataset) / 2 , 3*d3.max(dataset) / 4, d3.max(dataset)])

            .range(["#9c9ede","#6b6ecf","#5254a3", "#393b79"]);

So the code divide the value into 4 range, if the value smaller than 1/4 max value, then it use #9c9ede color;
from 1/4 - 1/2: #6b6ecf
...
from 3/4 - 1: #393b79

 var q = d3.scale.quantize().domain([0, 1]).range(['a', 'b', 'c']);

 //q(0.3) === 'a', q(0.4) === 'b', q(0.6) === 'b', q(0.7) ==='c';

 //q.invertExtent('a') returns [0, 0.3333333333333333]

[D3] 7. Quantitative Scales


### use:

.attr('fill', colorScale);

<!DOCTYPE html>

<html>

<head lang="en">

    <meta charset="UTF-8">

    <title></title>

    <script src="../bower_components/underscore/underscore-min.js"></script>

    <script src="../ventor/d3.min.js"></script>

    <style type="text/css">

        body

        {

            padding-top: 50px;

            padding-left: 100px;

        }

        #chartArea {

            width: 400px;

            height: 300px;

            background-color: #CCC;

        }

        .bar

        {

            display: inline-block;

            width: 20px;

            height: 75px; /* Gets overriden by D3-assigned height below */

            margin-right: 2px;

           /* fill: teal; *//* SVG doesn't have background prop, use fill instead*/

            z-index:99;

        }

    </style>

</head>

<body>

<section id="chartArea"></section>

<script>

    var dataset = _.map(_.range(30), function(num) {

        return Math.random() * 50;

    }), //reandom generate 15 data from 1 to 50

            w = 400, h = 300;

    var svg = d3.select('#chartArea').append('svg')

            .attr('width', w)

            .attr('height', h); //svg deosn't need 'px'

    var yScale = d3.scale.linear()

            .domain([0, d3.max(dataset) * 1.1]) //d3.max(dataset), set the max val of database

            .range([0, h]);

    var xScale = d3.scale.ordinal()

            .domain(dataset)

            .rangeBands([0,w],0.3, 0.1);

//    var colorScale = d3.scale.category20c();

    var colorScale = d3.scale.quantile()

            .domain([d3.max(dataset) / 4, d3.max(dataset) / 2 , 3*d3.max(dataset) / 4, d3.max(dataset)])

            .range(["#9c9ede","#6b6ecf","#5254a3", "#393b79"]);

    svg.selectAll('div')

            .data(dataset)

            .enter()

            .append('rect')// svg doesn't have div, use rect instead

            .attr('class', "bar")

            .attr('width', xScale.rangeBand())

            .attr('x', function(each_data, index){

                return xScale(each_data);

            })

            .attr('y', function(each_data){

                return h-yScale(each_data);

            })

            .attr('height', function(each_data, i){

                return yScale(each_data);

            })

            .attr('fill', colorScale);

</script>

</body>

</html>