Box Plot in Plotly

Last Updated: 08 Nov 2025

Box plots (or box-and-whisker plots) show data distribution through quartiles — perfect for comparing groups, detecting outliers, exam results, or sensor readings.

Hinglish Tip: Box plot = "5-number summary" — min, Q1, median, Q3, max — ek jhalak mein data ka mood pata chal jata hai!

Basic Box Plot

import plotly.express as px
import numpy as np

# Sample exam scores
np.random.seed(42)
scores = np.random.normal(75, 10, 200)

fig = px.box(y=scores, title="Exam Scores - Box Plot")
fig.show()

Key Parameters in `px.box()`

Parameter	Values / Examples	Purpose
data_frame	df	Use Pandas DataFrame
x, y	Column names	Group (x), values (y)
color	Column name	Color by category
points	'all', 'outliers', False	Show raw data points
notched	True	Show confidence interval around median
hover_data	['name']	Extra info on hover
title	String	Chart title
labels	'y': 'Score'	Rename axes
orientation	'v', 'h'	Vertical or horizontal

Full Example: Compare Classes

import plotly.express as px
import pandas as pd
import numpy as np

# Sample data: 3 classes
np.random.seed(42)
class_a = np.random.normal(70, 12, 100)
class_b = np.random.normal(78, 8, 100)
class_c = np.random.normal(65, 15, 100)

# Add some outliers
class_a = np.append(class_a, [30, 95])
class_c = np.append(class_c, [100])

df = pd.DataFrame({
    'Score': np.concatenate([class_a, class_b, class_c]),
    'Class': ['A']*102 + ['B']*100 + ['C']*101
})

fig = px.box(
    df,
    x='Class',
    y='Score',
    color='Class',
    notched=True,
    points='outliers',  # Only show outliers
    title='Exam Scores by Class (Box Plot)',
    labels={'Score': 'Marks', 'Class': 'Class'},
    hover_data={'Score': ':.1f'}
)

fig.update_layout(
    showlegend=False,
    font=dict(size=12)
)

fig.show()

Hinglish Tip:

points='outliers' → sirf extreme students dikhao — teacher ko turant pata chalega kon fail/pass!

Horizontal Box Plot (`orientation='h'`)

fig = px.box(
    df, y='Class', x='Score',
    orientation='h',
    color='Class',
    title='Horizontal Box Plot (Better for long labels)'
)
fig.show()

Hinglish Tip: Horizontal → class names lambi ho toh overlap nahi hota!

Add Mean & Custom Styling

fig = px.box(df, x='Class', y='Score', color='Class', points='all')

# Add mean as diamond
fig.update_traces(
    boxpoints='all',
    jitter=0.3,
    pointpos=-1.8,
    marker=dict(size=5)
)

# Add mean line
fig.update_traces(meanline_visible=True, meanline_color="black", meanline_width=2)

fig.update_layout(title="Box Plot with All Points + Mean Line")
fig.show()

Combine with Violin Plot (Advanced)

import plotly.graph_objects as go

fig = go.Figure()

for cls in df['Class'].unique():
    fig.add_trace(go.Violin(
        x=df['Class'][df['Class'] == cls],
        y=df['Score'][df['Class'] == cls],
        name=cls,
        box_visible=True,
        meanline_visible=True
    ))

fig.update_layout(title="Violin + Box Plot (Distribution + Summary)")
fig.show()

Common Mistakes to Avoid

Mistake	Fix
Hide outliers	Use points='outliers' or 'all'
No notch → can't compare medians	Use notched=True
Too many points → messy	Use points='outliers' only
Vertical labels cut off	Use orientation='h'
Forget kaleido	pip install -U kaleido

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