6 Steps to Interactive Python Dashboards with Plotly Dash
 Converting your data visualizations to interactive dashboards

Lianne & Justin

Lianne & Justin

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python interactive dashboard dash tutorial
Source: Freepik

In this tutorial, you’ll learn how to create Python interactive dashboards with plotly Dash.

Web-based dashboards are a great way to display and share information with others. But it often involves complicated processes that only a team of web developers can achieve. As Python developers in data science, how can we build an interactive web application with data visualizations?

Plotly Dash is the go-to library. It empowers us to build beautiful looking, interactive, and easy to share dashboards, all in Python.

Following this tutorial, you’ll learn:

  • What is Dash
  • How to build the Dash app layout
  • How to include data visualization
  • How to add interactive features (callbacks)
  • How to run and display the dashboard

If you want a quick example of building dashboards with Python Dash, this tutorial will walk you through the process step-by-step.

Let’s get started!

Further learning: to learn more details and depth about Dash, please take our video course: Python Interactive Dashboards with Plotly Dash. It includes step-by-step explanations, more advanced functions, all with real-world dataset examples.

This tutorial assumes you have basic Python knowledge. If not, please take our FREE Python crash course for data science.

It also helps to have some knowledge of the pandas library. Check out Learn Python Pandas for Data Science: Quick Tutorial.

What is Dash?

Dash is a free Python library that’s built by the same company that created Plotly. With Dash, you can develop web-based, customizable, interactive dashboards, all in Python, without writing HTML or JavaScript.

Each Dash app has two main parts:

  • layout: determines the visual components displayed on the Dash app.
  • callback function: the function that connects the Dash components and defines their interactive features.

Now let’s go through an example to make an interactive data visualization using Dash.

Step #1: Exploring the dataset

Before building the Dash app, we need to explore the dataset. We recommend doing this in Jupyter Notebook. Since it has an interactive interface, we can code and examine the results easily.

First, we’ll import two libraries:

  • pandas: for loading and manipulating datasets.
  • plotly.express: for generating data visualizations.
    Dash is built on top of plotly, so it’s easy to put plotly figures into Dash apps. This is why we are using plotly, instead of other Python data visualization libraries.

In this tutorial, we’ll use the Avocado Prices dataset to build our example dashboard. So let’s load it and take a look at its summary.

As you can see, the dataset contains information about avocado prices.

<class 'pandas.core.frame.DataFrame'>
RangeIndex: 30021 entries, 0 to 30020
Data columns (total 13 columns):
 #   Column         Non-Null Count  Dtype  
---  ------         --------------  -----  
 0   date           30021 non-null  object 
 1   average_price  30021 non-null  float64
 2   total_volume   30021 non-null  float64
 3   4046           30021 non-null  float64
 4   4225           30021 non-null  float64
 5   4770           30021 non-null  float64
 6   total_bags     30021 non-null  float64
 7   small_bags     30021 non-null  float64
 8   large_bags     30021 non-null  float64
 9   xlarge_bags    30021 non-null  float64
 10  type           30021 non-null  object 
 11  year           30021 non-null  int64  
 12  geography      30021 non-null  object 
dtypes: float64(9), int64(1), object(3)
memory usage: 3.0+ MB

Suppose we want to present the average prices of different types of avocados for various geographies across time, i.e., we want to focus on presenting the information of the features date, average_price, type, and geography.

What are the different type and geography of avocados? Let’s take a look at the categories using the value_counts method with dropna = False. This will show us the unique categories for these variables and if there are any missing values.

There are two categories of type, and many different categories for geography. And both variables don’t have missing values.

conventional    15012
organic         15009
Name: type, dtype: int64
Phoenix/Tucson          556
Northeast               556
Las Vegas               556
Sacramento              556
Tampa                   556
Spokane                 556
Southeast               556
New York                556
Raleigh/Greensboro      556
Syracuse                556
Plains                  556
California              556
Orlando                 556
Albany                  556
Boise                   556
Boston                  556
Houston                 556
West                    556
Portland                556
Harrisburg/Scranton     556
Cincinnati/Dayton       556
Miami/Ft. Lauderdale    556
Dallas/Ft. Worth        556
Hartford/Springfield    556
Great Lakes             556
Louisville              556
Philadelphia            556
Pittsburgh              556
Baltimore/Washington    556
Roanoke                 556
Jacksonville            556
Midsouth                556
Chicago                 556
San Francisco           556
South Central           556
San Diego               556
Detroit                 556
Grand Rapids            556
Nashville               556
Charlotte               556
Seattle                 556
Los Angeles             556
Northern New England    556
Indianapolis            556
Buffalo/Rochester       556
Total U.S.              556
Richmond/Norfolk        556
New Orleans/Mobile      556
Denver                  556
St. Louis               556
Atlanta                 556
South Carolina          556
Columbus                556
West Tex/New Mexico     553
Name: geography, dtype: int64

Since there are only two avocados types, we can plot their average_price time series on the same line chart.

Let’s try to plot such a figure when geography is ‘Los Angeles’.

Further Learning: If you are not familiar with plotly, please look at our tutorial Plotly Python Tutorial: How to create interactive graphs.
If you are not familiar with pandas filtering, please take a look at Learn Python Pandas for Data Science: Quick Tutorial.

python interactive dashboard dash tutorial plotly figure

This is a nice chart, but it’s only for one geography.

How can we make it easy for users to explore this information for different geography?

If we have a dropdown with options of geography, the users would be able to choose among them. Then according to the geography selected by the users, we can display the above line plot to them for that specific geography.

While this is not possible with plotly, it’s something Dash can help!

It’s time to use Dash.

Step #2: Setting up the Python environment

After exploring the dataset in Jupyter Notebook, we recommend using one of the Python editors to implement Dash apps. When working on Dash apps, we want to focus on building and running the dashboards as a whole script. So it’s easier to test in Python editors such as PyCharm.

We’re using the PyCharm Editor – Community Edition. It’s free and has many useful features for writing code in Python. But you’ll also be good to choose your preferred Python editor.

It’s also necessary to use the pip install dash command in your terminal to install Dash before using it.

Step #3: Preparing to build the Dash app

Now we can head over to the Python editor such as PyCharm to start writing the Dash app. The code snippets below need to be combined and run as a single Python script. We are breaking them down into pieces so that it’s easier to explain. You can either type them into your Python script or copy and paste the complete version, which will be provided at the end.

First, we need to import the libraries. The necessary libraries for our dashboard are:

  • dash: the main Dash library.
    Also importing Input, Output from dash.dependencies, so that we can use them without referring to dash.dependencies.
  • dash_html_components: for building the layout, which contains components for every HTML tag, such as the H1 heading.
  • dash_core_components: for building the layout, which contains various higher-level components such as dropdown, graph.
  • pandas: for loading and manipulating datasets.
  • plotly.express: for creating figures.

Then we can load the dataset as a pandas DataFrame, which is the same as earlier. Please make sure you save the Python script and the dataset avocado-updated-2020.csv in the same directory to avoid setting the path in the read_csv function.

We’ll also create a Dash app object called app as below. This app is what we’ll be focusing on for the rest of the tutorial.

Step #4: Building the layout of the dashboard

The app-building process always starts from the layout. We need to design the look of the dashboard first.

The layout has the structure of a tree of components. We use the keyword layout of the app to specify its layout. Then, using the two libraries: dash_html_components (html) and dash_core_components (dcc), we can display three components on our dashboard:

  • an H1 heading (html.H1) as the title of the dashboard. We specify its children property to be the text ‘Avocado Prices Dashboard’.
  • a dropdown menu (dcc.Dropdown) based on the geography.
    We give it an id ‘geo-dropdown’.
    The options property specifies the options of unique geographies the dropdown has.
    The value property is the selected geography when we first launch the app. We made it as ‘New York’.
  • a graph component (dcc.Graph) with id ‘price-graph’.

Below is the code to set up the layout.

As you noticed, we are using an html.Div component to hold our three Dash components. The html.Div is a container component, which is always used when we have multiple Dash components in the layout. We put the other Dash components as a list inside its children property.

After setting up the dashboard’s look, it’s time to add a callback function to make it interactive.

Step #5: Adding interactivity to the dashboard

The callback functions are Python functions. But they get automatically called by Dash whenever its input changes. As a result, the function runs and updates its output.

The two main sections of the callback function are:

  • the decorator which starts with @app.callback
  • the function itself starts with def

Below is the code of our callback function to make the plotly figure dependent on the dropdown.

Within the decorator @app.callback, we specify the Output and the Input objects of the callback function. They are both the properties of Dash components. In our example, the output is the figure property of the Dash component with ID = ‘price-graph’, which is the dcc.Graph component set in the layout. While the input is the value property of the Dash component with ID = ‘geo-dropdown’, which is the dcc.Dropdown component set in the layout.

After specifying them, we use them within the function below. Within the parenthesis after the def update_graph, we named the input as selected_geography, this corresponds to the Input(component_id='geo-dropdown', component_property='value'). Then within the body of the function, we ask the function to:

  • generate a filtered dataset filtered_avocado based on selected_geography
  • create a plotly line figure called line_fig based on this filtered dataset

The function returns this line_fig as the output, which corresponds to Output(component_id='price-graph', component_property='figure').

For example, when the user selects ‘Los Angeles’ in the dropdown component, its value property will become ‘Los Angeles’, which means the input of the function selected_geography='Los Angeles'. This change will trigger the callback function, and update the output, as the line figure only for Los Angeles.

That’s all the work needed for the callback function!

We are ready to run the dashboard.

Step #6: Running the dashboard

To complete the script, we need to add code to run the server. By default, the Dash app runs on our local computers. We can add these two lines of code after the callback function.

The complete script we need to save into the Python editor is below:

As mentioned earlier, we need to run it as a whole script. So we can save this whole block of code as a Python script (named avocado_example) under the same directory as our dataset avocado-updated-2020.csv. Then we can go to the terminal to run it by typing in the command python avocado_example.py.

After running successfully, you should see the below messages in the terminal window.

Dash is running on

 * Serving Flask app "avocado_example" (lazy loading)
 * Environment: production
   WARNING: This is a development server. Do not use it in a production deployment.
   Use a production WSGI server instead.
 * Debug mode: on

Remember that Dash creates web applications? So this URL is the default address to access the app. You can click this link and see your first Python interactive dashboard opening in the browser!

It should look like this:

dash interactive python dashboard example plotly graph

If you haven’t got the chance to run your app, take a look here. We have deployed this app on Heroku so that you can interact with it as a user. Try to select different geographies within the dropdown and see the updated graph.

That’s it!

In this tutorial, you’ve learned how to create your first Python interactive dashboard with Dash!

Again, to learn about how to:

  • set up more Dash components such as range slider, radio items, datatable
  • customize the look of the dashboards
  • create a grid layout dashboard
  • more dynamic interactive features

please take our video-format course: Python Interactive Dashboards with Plotly Dash. You’ll also get an overview of HTML, CSS within the course, so you’ll have a better understanding of Dash.

Leave a comment for any questions you may have or anything else.

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