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DC.js – Line Chart

DC.js - Line Chart

A Dc.js line chart is used to display information as a series of data points connected by straight lines. A data point represents two values, one plotted along the horizontal axis and another along the vertical axis. For example, the popularity of food items can be drawn as a line chart in such a way that the food item is represented along the x-axis and its popularity is represented along the y-axis. This chapter explains about line charts in detail.

Line Chart Methods

Before moving on to draw a line chart of DC.js, we should understand the dc.lineChart class and its methods. The dc.lineChart uses mixins to get the basic functionality of drawing a chart. The mixins used by dc.lineChart are as follows −

  • dc.stackMixin
  • dc.coordinateGridMixin

The complete class diagram of the dc.lineChart is as follows −

DC.js - Line Chart

The dc.lineChart gets all the methods of the above-specified mixins as well as it has its own methods to draw the line chart. They are explained as follows.

dashStyle( [style])

This method is used to set the dash style for a line chart.

dotRadius( [radius])

This method is used to get or set the radius (in PX) for dots displayed on the data points. It is defined as follows −

chart.dotRadius = function (radius) {
   if (!arguments.length) {
      return radius;
   }
};

interpolate( [i])

This method is used to get or set the interpolator for a line.

renderArea( [area])

This method is used to get or set the render area.

renderDataPoints( [options])

This method is used to render individual dots for each data point.

tension( [tension])

This method is used get or set the tension for the lines drawn. It is in the range from 0 to 1.

xyTipsOn( [xyTipsOn])

This method is used to change the mouse behavior of an individual data point.

Draw a Line Chart

Let us draw a line chart in DC. To do this, we need to follow the steps given below −

Step 1: Define a variable

Let us define a variable as shown below −

var chart = dc.lineChart('#line');

Here, the dc.linechart function is mapped with the container having an id line.

Step 2: Read the data

Read data from the people.csv file −

d3.csv("data/people.csv", function(errors, people) {
   var mycrossfilter = crossfilter(people);
}

Here, if we used the same dataset people.csv, the sample data file will be as follows −

id,name,gender,DOB,MaritalStatus,CreditCardType
1,Damaris,Female,1973-02-18,false,visa-electron
2,Barbe,Female,1969-04-10,true,americanexpress
3,Belia,Female,1960-04-16,false,maestro
4,Leoline,Female,1995-01-19,true,bankcard
5,Valentine,Female,1992-04-16,false,
6,Rosanne,Female,1985-01-05,true,bankcard
7,Shalna,Female,1956-11-01,false,jcb
8,Mordy,Male,1990-03-27,true,china-unionpay

...............
................
................

Step 3: Create an age dimension

Now, create dimension for age as shown below −

var ageDimension = mycrossfilter.dimension(function(data) { 
    return ~~((Date.now() - new Date(data.DOB)) / (31557600000)) 
});

Here, we assigned the age from the Crossfilter data.

The ~~ is a double NOT bitwise operator. It is used as a faster substitute for the Math.floor() function.

Now, group it using the reduceCount() function, which is defined below −

var ageGroup = ageDimension.group().reduceCount();

Step 4: Generate a chart

Now, generate a line chart using the coding given below −

chart
   .width(800)
   .height(300)
   .x(d3.scale.linear().domain([15,70]))
   .brushOn(false)
   .yAxisLabel("Count")
   .xAxisLabel("Age")
   .dimension(ageDimension)
   .group(ageGroup)
   .on('renderlet', function(chart) {
      chart.selectAll('rect').on('click', function(d) {
         console.log('click!', d);
      });
   });

chart.render();

Here,

  • Chart width is 800 and height is 300.
  • The d3.scale.linear function is used to construct a new linear scale with the specified domain range [15, 70].
  • Next, we set the brushOn value to false.
  • We assign the y-axis label as count and x-axis label as age.
  • Finally, group the age using ageGroup.

Step 5: Working example

The complete code listing is shown in the following code block. Create a web page line.html and add the following changes to it.

<html>
   <head>
      <title>DC.js Line Chart Sample</title>
      <link rel = "stylesheet" type = "text/css" href = "css/bootstrap.min.css">
      <link rel = "stylesheet" type = "text/css" href = "css/dc.css"/>

      <script src = "js/d3.js"></script>
      <script src = "js/crossfilter.js"></script>
      <script src = "js/dc.js"></script>
   </head>
   
   <body>
      <div>
         <div id = "line"></div>
      </div>

      <script language = "javascript">
         var chart = dc.lineChart('#line');

         d3.csv("data/people.csv", function(errors, people) {
            var mycrossfilter = crossfilter(people);

            var ageDimension = mycrossfilter.dimension(function(data) { 
               return ~~((Date.now() - new Date(data.DOB)) / (31557600000)) 
            });
            var ageGroup = ageDimension.group().reduceCount();

            chart
               .width(800)
               .height(300)
               .x(d3.scale.linear().domain([15,70]))
               .brushOn(false)
               .yAxisLabel("Count")
               .xAxisLabel("Age")
               .dimension(ageDimension)
               .group(ageGroup)
               .on('renderlet', function(chart) {
                  chart.selectAll('rect').on('click', function(d) {
                     console.log('click!', d);
                  });
               });
            chart.render();
         });
      </script>
   </body>
</html>

Now, request the browser and we will see the following response.

30

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