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Pattern hatching texture

New in v5.0

Bar charts, histograms and polar bar charts have large markers which support not only a fill color, but also an optional pattern (also known as "hatching" or "texture"). This can be used for a variety of reasons:

  • to double-encode variables (i.e. using both color and pattern) to improve accessibility for visually-impaired end-users
  • to encode an additional variable beyond just using color
  • to make charts that are easier to print in black and white

Patterned Bar Charts with Plotly Express

the px.bar(), px.histogram() and px.bar_polar() functions support the pattern_shape argument. In the chart below, we double-encode nation using color and pattern:

import plotly.express as px
df = px.data.medals_long()

fig = px.bar(df, x="medal", y="count", color="nation", pattern_shape="nation")
fig.show()

In the chart below we use px.histogram() instead of px.bar() to aggregate multiple values together, and encode one variable (sex) using both color and x-position and another (smoker) using patterns:

import plotly.express as px

df = px.data.tips()
fig = px.histogram(df, x="sex", y="total_bill", color="sex", pattern_shape="smoker")
fig.show()

Controlling Pattern Assignment

In the charts above, the first value of the variable assigned pattern_shape gets the empty pattern, but this (and indeed every pattern-to-variable assignment) can be controlled using pattern_shape_sequence and pattern_shape_map, analogously to the way discrete colors can be mapped using Plotly Express.

Here we use pattern_shape_sequence to replace the defaults and include a pattern-shape for the first variable:

```python tags=[] import plotly.express as px df = px.data.medals_long()

fig = px.bar(df, x="medal", y="count", color="nation", pattern_shape="nation", pattern_shape_sequence=[".", "x", "+"]) fig.show() 

Here we use `pattern_shape_map` to explictly assign a shape to each value of `nation`, regardless of order:

```python
import plotly.express as px
df = px.data.medals_long()

fig = px.bar(df, x="medal", y="count", color="nation",
             pattern_shape="nation", pattern_shape_map={
             "China": ".", "Canada": "/", "South Korea": "+"
             })
fig.show()

Black on White Patterns for Print

When creating figures meant to be printed on black and white printers, it is better to replace the fill-color with the pattern, rather than to overlay it. This can be controlled with the <trace>.marker.pattern.fillmode attribute, which defaults to "overlay" but can be set to "replace" instead. Changing this attribute, and using a simpler default template and color scheme gives the following output:

import plotly.express as px
df = px.data.medals_long()

fig = px.bar(df, x="medal", y="count", color="nation",
             pattern_shape="nation", pattern_shape_sequence=[".", "x", "+"],
             template="simple_white"
            )
fig.update_traces(
    marker=dict(color="black", line_color="black", pattern_fillmode="replace")
)
fig.show()

Of course, this setting can be used without making the figure monochrome as well:

import plotly.express as px
df = px.data.medals_long()

fig = px.bar(df, x="medal", y="count", color="nation",
             pattern_shape="nation", pattern_shape_sequence=[".", "x", "+"],
            )
fig.update_traces(
    marker=dict(line_color="grey", pattern_fillmode="replace")
)
fig.show()

Patterns using Graph Objects

If Plotly Express does not provide a good starting point, it is also possible to use the more generic go.Bar class from plotly.graph_objects.

import plotly.graph_objects as go

fig = go.Figure()

fig.add_trace(go.Bar(x=["a","b"], y=[1,2], marker_pattern_shape="."))
fig.add_trace(go.Bar(x=["a","b"], y=[3,1], marker_pattern_shape="x"))
fig.add_trace(go.Bar(x=["a","b"], y=[2,3], marker_pattern_shape="+"))

fig.show()

Reference

See https://plotly.com/python/reference/bar/ for more information and chart attribute options!

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