[D3] 7. Quantitative Scales

清疚 2022-03-31 17:50 39阅读 0赞

# 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]

![041526095667736.png][]

### 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>

[041526095667736.png]: /images/20220331/0ce3c9c286c4426e919b1f02bab8443f.png