Data Loading in D3.js

The term data loading refers to the “load” element of ETL (Extract Transform Load). After the retrieving and merging data from various resources, it will be transformed, cleaned, and formatted. Now it is loaded into the storage system such as a cloud data warehouse. D3.js facilitate to manage the various types of data determined from an external file or a variable. In this lesson, we will discuss the data loading from various files and wrap it to the DOM elements.

Methods of Data Loading

In D3.js, some methods help you to load the data from the various types of files. These methods are listed below.  

  • d3.json()
  • d3.csv
  • d3.xml
  • d3.tsv

Let’s explain each of these in detail.

d3.json()

This method can be applied to sends the http request over to a stated URL for loading .json file or data. It also compiles the callback function among with the parsed data object of the json file. The JSON data can be an individual object or an array of objects.

The working procedure of the JSON is similar to CSV. The d3.json() accepts a JSON file as an input and transform it in the form of an array object.

Syntax

In the above syntax, we have two parameters; the first is a .json file, and the second is a callback function, it will be compiled during the loading of the .json file. This function passes the parsed data object in the form of a parameter over to a callback function.   

Example

Here, you need to create a simple json file named user.json and save it in the root folder of the d3 folder.

[/crayon] ”name” :”John” ,[/crayon] ”age” : 30,[/crayon] ”city” :”New York” [/crayon] ”name” :”Jane” ,[/crayon] ”age” : 20,[/crayon] ”city” :”San Francisco” [/crayon]

Now, you need to load the JSON file with the help of the d3.json() method, as explained in the below script.

d3.json(“data/user.json”, function(data)

{

            Console.log(data);

});

Output

After the execution of the above code on the browser, you got the following code.

d3.csv

This method can be applied to send the http request over to a stated URL for loading the .csv file or data. It also compiles the callback function among with the parsed data object of csv file. You can load the csv data or file with the help of the d3.csv() method.

Syntax

d3.csv(url[, row, callback]);

The syntax contains the three following parameters.

.csv url: It is a first parameter used to return the csv data. It is also called webapi, web service.

row: This parameter is a transformation function that helps you to modify the presentation. It is optional to use.

callback function: The callback function will be executed only once during the csv file or data loading. This function passes the parsed data object in the form of a parameter over to a callback function.  

Example

Here, we consider an example to understand the loading of csv data, stored in the below-given file.

employee.csv

Name, Age

John, 30

Jane, 32

Now you are required to store the above file, the root folder of d3. It is shown in the below-mentioned script.

<script>                        // Loading csv data

d3.csv(“data/employees.csv”, function(data)

{

            for (var i=0;i<data.length; i++)

{

            console.log(data[i].Name);

            console.log(data[i].Age);

}

});

</script>

Output

After executing the above code on the browser, you got the below-shown output in the developer option.

In the above example, you can see that d3.csv() function stores a file name as an input, operates the file, and load the file data into an object’s array.

NOTE: The first row of the program file doesn’t print because it is considered as the name of the column and remaining rows are treated as a data file. D3 takes the name of column as the properties of the objectand then transforms them into the keys of the object.

d3.xml

This method will be used to send a request to the webserver to the link provided for loading .csv file or information. It also compiles the callback function for the interpreted data object of the csv format. d3.xml () method helps you to obtain XML’s file URL, and it also returns an object of xml.

Syntax

Example  

Here, we consider an example to elaborate the d3.xml() method.

<?xml version = “1.0” encoding = “UTF-8”?>

<root>

<row>

<Name>John</Name>

<Age>30</Age>

</row>

<row>

<Name>Jane</Name>

<Age>32</Age>

</row>

</root>

d3.xml(“/data/employee.xml”, function(data)                             // xml data loading

{

            console.log(data);

});

You can also perform traversing and parsing with the help of the below-mentioned script.

d3.xml(“\data\employee.xml”, function(data)

{

            console.log(xml.documentElement.getElementByTagName(“Name”, ”));

}); 

Output

After the execution of the above code, you got the following output.

The output returns you all the tags with the tag name.

d3.tsv

This method will be used to send a request to the webserver to the link provided for loading .tsv file or information. It also compiles the callback function for the interpreted data object of the tsv format. The d3.tsv () method obtains a tsv file in the form of input url, and after parsing, it returns a data object of a specific file.

Syntax

d3.tsv(url, callback);

Example

Here, we consider an example to elaborate on the d3.tsv() method.

employees.tsv

Name, Age

John, 30

Jane, 32

Now, you are required to fetch the tsv file and perform the data parsing with the help of the d3.tsv() method. It is explained in the below code.

d3.tsv(“/data/employees.tsv”, function(data)                 // Loading tsv data

{

            for(var i = 0; i< data.length; i++)

{

            console.log(data[i]>Name);

            console.log(data[i]>Age);

}

});

Output

After the execution of the above code, you got the following output.

Loaded Data Binding

After loading the data, you are able to work with the data objects. Here, we implement the data stored in the JSON file named users.json. It is shown in the below figure.

users.json

[{

    “name”: “Jon”,

    “age”: 30,

    “location”: “The Wall”

},

{

    “name”: “Arya”,

    “age”: 12,

    “location”: “Braavos”

},

{

    “name”: “Cersei”,

    “age”: 42,

    “location”: “Kings Landing”

},

{

    “name”: “Tyrion”,

    “age”: 40,

    “location”: “Kings Landing “

}]

Now, we load the .json file with the help of the d3.json() method. We also wrap it with the elements of DOM.

Example

d3.json(“/data/users.json”, function(error, data) {

    d3.select(“body”)

        .selectAll(“p”)

        .data(data)

        .enter()

        .append(“p”)

        .text(function(d) {

            return d.name + “, ” + d.location;

        });

});

Output

After the execution of the example, you got the following output.

Error Handling

Error management refers to the prediction, identification, and correction of programming, implementation, and coordination errors. Specialized systems, known as error handlers, are available for specific applications.

For Example

Here, we have an illustration of the above concept.

d3.json(“/data/users.json”, function(error, data) {

    if (error) {

        return console.warn(error);

    }

    d3.select(“body”)

            .selectAll(“p”)

            .data(data)

            .enter()

            .append(“p”)

            .text(function(d) {

                return d.name + “, ” + d.location;

            });

    });

If there is any error during the data loading, then d3 returns an object representing an error. You are required to check the errors. Thus, you can load the data from the multiple files.