figure-labels.md

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Automatic Labelling with Plotly Express

Plotly Express is the easy-to-use, high-level interface to Plotly, which operates on a variety of types of data and produces easy-to-style figures.

When using Plotly Express, your axes and legend are automatically labelled, and it's easy to override the automation for a customized figure using the labels keyword argument. The title of your figure is up to you though!

Here's a figure with automatic labels and then the same figure with overridden labels. Note the fact that when overriding labels, the axes, legend title and hover labels reflect the specified labels automatically.

import plotly.express as px

df = px.data.iris()
fig = px.scatter(df, x="sepal_length", y="sepal_width", color="species",
                title="Automatic Labels Based on Data Frame Column Names")
fig.show()

import plotly.express as px

df = px.data.iris()
fig = px.scatter(df, x="sepal_length", y="sepal_width", color="species",
                 labels={
                     "sepal_length": "Sepal Length (cm)",
                     "sepal_width": "Sepal Width (cm)",
                     "species": "Species of Iris"
                 },
                title="Manually Specified Labels")
fig.show()

Global and Local Font Specification

You can set the figure-wide font with the layout.font attribute, which will apply to all titles and tick labels, but this can be overridden for specific plot items like individual axes and legend titles etc. In the following figure, we set the figure-wide font to Courier New in blue, and then override this for certain parts of the figure.

import plotly.express as px

df = px.data.iris()
fig = px.scatter(df, x="sepal_length", y="sepal_width", color="species",
                title="Playing with Fonts")
fig.update_layout(
    font_family="Courier New",
    font_color="blue",
    title_font_family="Times New Roman",
    title_font_color="red",
    legend_title_font_color="green"
)
fig.update_xaxes(title_font_family="Arial")
fig.show()

Manual Labelling with Graph Objects

When using (graph objects)[/python/graph-objects/] rather than Plotly Express, you will need to explicitly label traces and axes:

import plotly.graph_objects as go

fig = go.Figure()

fig.add_trace(go.Scatter(
    x=[0, 1, 2, 3, 4, 5, 6, 7, 8],
    y=[0, 1, 2, 3, 4, 5, 6, 7, 8],
    name="Name of Trace 1"       # this sets its legend entry
))


fig.add_trace(go.Scatter(
    x=[0, 1, 2, 3, 4, 5, 6, 7, 8],
    y=[1, 0, 3, 2, 5, 4, 7, 6, 8],
    name="Name of Trace 2"
))

fig.update_layout(
    title="Plot Title",
    xaxis_title="X Axis Title",
    yaxis_title="X Axis Title",
    legend_title="Legend Title",
    font=dict(
        family="Courier New, monospace",
        size=18,
        color="RebeccaPurple"
    )
)

fig.show()

The configuration of the legend is discussed in detail in the Legends page.

Align Plot Title

The following example shows how to align the plot title in layout.title. x sets the x position with respect to xref from "0" (left) to "1" (right), and y sets the y position with respect to yref from "0" (bottom) to "1" (top). Moreover, you can define xanchor to left,right, or center for setting the title's horizontal alignment with respect to its x position, and/or yanchor to top, bottom, or middle for setting the title's vertical alignment with respect to its y position.

import plotly.graph_objects as go

fig = go.Figure(go.Scatter(
    y=[3, 1, 4],
    x=["Mon", "Tue", "Wed"]))

fig.update_layout(
    title={
        'text': "Plot Title",
        'y':0.9,
        'x':0.5,
        'xanchor': 'center',
        'yanchor': 'top'})

fig.show()

Reference

See https://plotly.com/python/reference/layout/ for more information!