DC.js - Data Count

Data count is used to display the total number of records in the data set. It performs the following two types of count −

  • Total-count − total number of records.

  • Filter-count − number of records matched by the current filters.

Data Count Methods

Before moving on to use a data count, we should understand the dc.dataCount class and its methods. The dc.dataCount class uses a mixin to get the basic functionality of displaying a data count, which is −

  • dc.baseMixin

The dc.dataCount gets all the methods of this mixin and has its own method to show the data count as explained below −

formatNumber( [formatter])

This method is used to get or set a format for the filter count and the total count.

html( [options])

It is used get or set the HTML templates to show the number of selected items.

For example −

counter.html ({
   all: 'HTML template to use if all items are selected'
})

Here, ‘all’ is used to select all the items using the %total-count. If we want to only use some of the items, then we can use some records using %filter-count option.

Data count example

Let us perform the data count in DC. To do this, we need to follow the steps given below −

Step 1: Add styles

Let us add styles in the CSS using the coding given below −

.dc-chart { font-size: 12px; }

Here, we have assigned styles for the chart.

Step 2: Create a variable

Let us create a variable in DC as shown below −

var barChart = dc.barChart('#line'); 
var countChart = dc.dataCount("#mystats");

Here, we have assigned a barChart variable id in line, whereas the countChart id is mystats.

Step 3: Read the data

Read the data from the people.csv file as shown below −

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

If the data is not present, then it returns an error. Now, assign the data to a crossfilter.

Here, we are using the people.csv file, which was used in our previous charting examples. It looks as shown below −

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 4: Set the dimension

You can set the dimension using the coding given below −

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

After the dimension has been assigned, group the age using the coding given below −

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

Step 5: Generate a chart

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

barChart
   .width(400)
   .height(200)
   .x(d3.scale.linear().domain([15,70]))
   .yAxisLabel("Count")
   .xAxisLabel("Age")
   .elasticY(true)
   .elasticX(true)
   .dimension(ageDimension)
   .group(ageGroup);

Here,

  • We have assigned the chart width as 400 and height as 200.
  • Next, we have specified the domain range as [15,70].
  • We have set the x-axis label as age and y-axis label as count.
  • We have specified the elasticY and X function as true.

Step 6: Create and render the count chart

Now, create and render the count chart using the coding below −

countChart
   .dimension(mycrossfilter)
   .group(mycrossfilter.groupAll());

barChart.render();
countChart.render();

Here, we have assigned the dimension to a crossfilter variable. Finally, group all the records based on the age.

Step 7: Working example

The complete code is as follows. Create a web page datacount.html and add the following changes to it.

<html>
   <head>
      <title>DC datacount sample</title>
      <link rel = "stylesheet" type = "text/css" href = "css/bootstrap.css" />
      <link rel = "stylesheet" type = "text/css" href = "css/dc.css" />
   
      <style>
         .dc-chart { font-size: 12px; }
      </style>

      <script src = "js/d3.js"></script>
      <script src = "js/crossfilter.js"></script>
      <script src = "js/dc.js"></script>
   </head>
   
   <body>
      <div>
         <div style = "width: 600px;">
            <div id = "mystats" class = "dc-data-count" style = "float: right">
               <span class = "filter-count"></span> selected out of <span
                  class = "total-count"></span> | <a href = "javascript:dc.filterAll();
                  dc.renderAll();">Reset All</a>
            </div>
         </div>

         <div style = "clear: both; padding-top: 20px;">
            <div>
               <div id = "line"></div>
            </div>
         </div>
      </div>

      <script language = "javascript">
         var barChart = dc.barChart('#line'); // , 'myChartGroup');
         var countChart = dc.dataCount("#mystats");

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

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

            barChart
               .width(400)
               .height(200)
               .x(d3.scale.linear().domain([15,70]))
               .yAxisLabel("Count")
               .xAxisLabel("Age")
               .elasticY(true)
               .elasticX(true)
               .dimension(ageDimension)
               .group(ageGroup);

            countChart
               .dimension(mycrossfilter)
               .group(mycrossfilter.groupAll());

            barChart.render();
            countChart.render();
         });
      </script>
   </body>
</html>

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

Data count initial page is shown below.

After selecting a particular age, it shows the counts as shown in the screenshot below.

Data Count
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