Customizing hover information and legends

Introduction to Data Visualization with Plotly in Python

Alex Scriven

Data Scientist

What do we mean by hover?

Hover information: The text and data that appear when your mouse moves over a data point

Default hover option

Other default hover information

By default hovermode = "closest"

"x" or "y": adds a highlight on the x or y axis

"x unified" / "y unified": displays a line and a hover box showing all values on the x or y axis

x hover

X unified hover

Hover information using plotly.express

hover_name = A specified column that will appear in bold at the top of the hover box

hover_data = A list of columns to include or a dictionary to include/exclude columns
- {column_name: False} (this will exclude column_name)

Variables in hover information

💡 Hover columns don't need to be in the plot

fig = px.scatter(revenues, 
        x="Revenue", 
        y="employees",
        hover_name="Company",
        hover_data=["age"])

fig.show()

Hover over scatterplot

Styling hover information

hoverlabel
- Accepts a dictionary of style properties like font, background color, and alignment

hovertemplate
- HTML-like string to format the text (beyond this course)

What is a legend?

A visual guide that helps explain elements in your plot, like color or symbol

Usually added automatically when needed
- For example, when adding colors to our bar chart

Bar chart with colors

Creating and styling the legend

Use update_layout() to control the legend

showlegend = True displays the default legend
legend - takes a dictionary of properties
- x, y let us position the legend within the plot area (range from 0 to 1)
- Other stylistic elements such as bgcolor (background color), borderwidth, and font

Check the documentation for more

A styled legend

fig.update_layout(
    "showlegend": True,

    legend_title_text="All Companies"

    legend=dict(
    x=0.7, y=0.8,
    bgcolor="rgb(246,228,129)"))
})

A Styled legend

Let's practice!

Introduction to Data Visualization with Plotly in Python