Plotly box plot with multiple categories

Question

Consider the following toy data:

import pandas as pd
import numpy as np
from plotly import graph_objects as go
from plotly.subplots import make_subplots

np.random.seed(42)

df = pd.DataFrame(
    {
        "val1": np.random.normal(0, 1, size=100),
        "val2": np.random.normal(5, 2, size=100),
        "cat": np.random.choice(["a", "b"], size=100),
    }
)

which yields (top 5 rows):

	val1	val2	cat
0	0.496714	2.16926	b
1	-0.138264	4.15871	b
2	0.647689	4.31457	a
3	1.52303	3.39545	b
4	-0.234153	4.67743	a

My objective is to get two box plots each containing two boxes (one per category).

Following code:

fig = make_subplots(rows=2, cols=1, subplot_titles=["Value 1 dist", "Value 2 dist"])

fill_colors = {"a": "rgba(150, 25, 40, 0.5)", "b": "rgba(25, 150, 40, 0.5)"}

for i, val in enumerate(["val1", "val2"]):
    for c in df["cat"].unique():
        dff = df[df["cat"] == c]
        fig.add_trace(
            go.Box(
                y=dff[val],
                x=dff["cat"],
                boxmean="sd",
                name=c,
                showlegend=True if val=="val1" else False,
                fillcolor=fill_colors[c],
                line={"color": fill_colors[c]},
            ),
            row=i + 1,
            col=1,
        )

Brings me very close:

Here are the things I would like to adjust:

How do I get, programmatically, the first 2 (or n) colors used in the default cycle of Plotly? So the result is compatible with other plots. Note that I hardcoded the colors...
The legend on the left; is there a more programmatic way to have only single legend? Note that I used showlegend=True if val=="val1" else False.
Bonus: How can I control the order of the boxes (i.e. which category comes first?)

I posted in the past two related questions (here and here) but the answers there didn't help me tune me plot as I want.

r-beginners · Accepted Answer · 2022-06-29 15:03:45Z

1

Please refer to the official reference for how to get the color names for a standard color set. You can get the color names in a list.
As for controlling duplicate legends, I personally don't have a problem with your method as I use it and it is a common approach, but if I were to handle it programmatically, I would use set() to make it unique by adding the duplicate legend names. I learned this Tips from this answer.
The third is to order by category, you can specify ascending or descending order by category.

This is a response from someone who did not get the expected answer. What was unsatisfactory about my previous answers? I will respond whenever possible.

import pandas as pd
import numpy as np
from plotly import graph_objects as go
from plotly.subplots import make_subplots
import plotly.express as px

# https://plotly.com/python/discrete-color/#color-sequences-in-plotly-express
plotly_default = px.colors.qualitative.Plotly
print(plotly_default)

fig = make_subplots(rows=2, cols=1, subplot_titles=["Value 1 dist", "Value 2 dist"])

fill_colors = {"a": plotly_default[0], "b": plotly_default[1]}

for i, val in enumerate(["val1", "val2"]):
    for c in df["cat"].unique():
        dff = df[df["cat"] == c]
        fig.add_trace(
            go.Box(
                y=dff[val],
                x=dff["cat"],
                boxmean="sd",
                name=c,
                showlegend=True, # if val=="val1" else False,
                fillcolor=fill_colors[c],
                line={"color": fill_colors[c]},
                opacity=0.5
            ),
            row=i + 1,
            col=1,
        )
names = set()
fig.for_each_trace(
    lambda trace:
        trace.update(showlegend=False)
        if (trace.name in names) else names.add(trace.name))

fig.update_xaxes(categoryorder='category ascending')
fig.update_layout(legend=dict(traceorder='reversed'))
fig.show()

edited Jun 29, 2022 at 15:03

answered Jun 29, 2022 at 13:55

r-beginners

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2 Comments

Dror Over a year ago

Regarding the color scheme. Using your approach turns the colors to solid ones. The default coloring behavior of go.Box is to have some opacity so the auxiliary lines will be visible. So maybe I'm asking the wrong question and the correct one is how go.Box colors by default.

r-beginners Over a year ago

If that is the case, we can add transparency. Is there anything else that needs to be corrected?

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