plotly.graph_objects.Heatmap

A heatmap refers to a type of plot that uses a cartesian plane where the data is represented as colored rectangular tiles.

This article will discuss creating heatmap plots using the Plotly graph_objects module.

Parameter and Syntax

To create a heatmap plot using plotly graph_objects, you can follow the following syntax:

plotly.graph_objects.Heatmap(arg=None, autocolorscale=None, colorbar=None, colorscale=None, x=None, y=None, z=None, **kwargs)

Parameter list:

Arg – This defines a dictionary with compatible properties with the Heatmap constructor.
autocolorscale – This sets whether the colorscale uses the default palette or determine by the colorscale parameter.
colorbar – A dictionary containing compatible properties of the colorbar instance.
colorscale – This determines the colorscale as an RGB, RGBA, hex, HSL, HSV, or named color string.
x – This sets the values for the x coordinate.
y – This defines the values for the y coordinate.
z – This sets the values for the z coordinate.

Basic Heatmap Using Plotly Graph Objects

The following code shows how to create a simple heatmap plot using Plotly graph_objects:

import plotly.graph_objects as go
fig = go.Figure(data=go.Heatmap(
z=[[1,2,3,
4,5 ,6,
7,8,9]]
))
fig.show()

The previous code should create a heatmap plot as follows:

Adding Axis Labels

We can add categorical axis labels by adding the x and y parameters, as shown in the following code:

An example output figure is as follows:

Adding Text on Heatmap Points

You can add text on heatmap points by specifying the text parameter, as illustrated in the following code:

import plotly.graph_objects as go
x = ['E1', 'E2', 'E3', 'E4', 'E5']
y = ['S1', 'S2', 'S3']
z = [[40.32, 43.33, 39.94], [40.12, 40.13, 43.12], [39.03, 40.23, 40.22]]

fig = go.Figure(data=go.Heatmap(
x=x,
y=y,
z=z,
text=[[40.32, 43.33, 39.94], [40.12, 40.13, 43.12], [39.03, 40.23, 40.22]],
texttemplate="%{text}",
textfont={"size": 10},
hoverongaps = False
))
fig.show()

Output figure:

Setting Colorscale

We can also specify a custom color scale by setting the colorscale parameter, as shown in the following code sample:

import plotly.graph_objects as go
import plotly.express as px
x = ['E1', 'E2', 'E3', 'E4', 'E5']
y = ['S1', 'S2', 'S3']
z = [[40.32, 43.33, 39.94], [40.12, 40.13, 43.12], [39.03, 40.23, 40.22]]

fig = go.Figure(data=go.Heatmap(
x=x,
y=y,
z=z,
text=[[40.32, 43.33, 39.94], [40.12, 40.13, 43.12], [39.03, 40.23, 40.22]],
texttemplate="%{text}",
textfont={"size": 10},
hoverongaps = False,
colorscale=px.colors.sequential.matter_r
))
fig.show()

The resulting figure is as follows:

Conclusion

This article describes creating a heatmap plot using the Plotly graph_objects module. We showed how to add axis labels, add text on heatmap points, and set colorscales.

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