Seaborn

Seaborn Statistical Visualization

Overview

Seaborn is a Python visualization library for creating publication-quality statistical graphics. Use this skill for dataset-oriented plotting, multivariate analysis, automatic statistical estimation, and complex multi-panel figures with minimal code.

Design Philosophy

Seaborn follows these core principles:

1. Dataset-oriented: Work directly with DataFrames and named variables rather than abstract coordinates
2. Semantic mapping: Automatically translate data values into visual properties (colors, sizes, styles)
3. Statistical awareness: Built-in aggregation, error estimation, and confidence intervals
4. Aesthetic defaults: Publication-ready themes and color palettes out of the box
5. Matplotlib integration: Full compatibility with matplotlib customization when needed

Quick Start

import seaborn as sns
import matplotlib.pyplot as plt
import pandas as pd

# Load example dataset
df = sns.load_dataset('tips')

# Create a simple visualization
sns.scatterplot(data=df, x='total_bill', y='tip', hue='day')
plt.show()

Core Plotting Interfaces

Function Interface (Traditional)

The function interface provides specialized plotting functions organized by visualization type. Each category has axes-level functions (plot to single axes) and figure-level functions (manage entire figure with faceting).

When to use:

• Quick exploratory analysis
• Single-purpose visualizations
• When you need a specific plot type

Objects Interface (Modern)

The seaborn.objects interface provides a declarative, composable API similar to ggplot2. Build visualizations by chaining methods to specify data mappings, marks, transformations, and scales.

When to use:

• Complex layered visualizations
• When you need fine-grained control over transformations
• Building custom plot types
• Programmatic plot generation

from seaborn import objects as so

# Declarative syntax
(
    so.Plot(data=df, x='total_bill', y='tip')
    .add(so.Dot(), color='day')
    .add(so.Line(), so.PolyFit())
)

Plotting Functions by Category

Relational Plots (Relationships Between Variables)

Use for: Exploring how two or more variables relate to each other

• scatterplot() - Display individual observations as points
• lineplot() - Show trends and changes (automatically aggregates and computes CI)
• relplot() - Figure-level interface with automatic faceting

Key parameters:

• x, y - Primary variables
• hue - Color encoding for additional categorical/continuous variable
• size - Point/line size encoding
• style - Marker/line style encoding
• col, row - Facet into multiple subplots (figure-level only)

# Scatter with multiple semantic mappings
sns.scatterplot(data=df, x='total_bill', y='tip',
                hue='time', size='size', style='sex')

# Line plot with confidence intervals
sns.lineplot(data=timeseries, x='date', y='value', hue='category')

# Faceted relational plot
sns.relplot(data=df, x='total_bill', y='tip',
            col='time', row='sex', hue='smoker', kind='scatter')

Distribution Plots (Single and Bivariate Distributions)

Use for: Understanding data spread, shape, and probability density

• histplot() - Bar-based frequency distributions with flexible binning
• kdeplot() - Smooth density estimates using Gaussian kernels
• ecdfplot() - Empirical cumulative distribution (no parameters to tune)
• rugplot() - Individual observation tick marks
• displot() - Figure-level interface for univariate and bivariate distributions
• jointplot() - Bivariate plot with marginal distributions
• pairplot() - Matrix of pairwise relationships across dataset

Key parameters:

• x, y - Variables (y optional for univariate)
• hue - Separate distributions by category
• stat - Normalization: "count", "frequency", "probability", "density"
• bins / binwidth - Histogram binning control
• bw_adjust - KDE bandwidth multiplier (higher = smoother)
• fill - Fill area under curve
• multiple - How to handle hue: "layer", "stack", "dodge", "fill"

# Histogram with density normalization
sns.histplot(data=df, x='total_bill', hue='time',
             stat='density', multiple='stack')

# Bivariate KDE with contours
sns.kdeplot(data=df, x='total_bill', y='tip',
            fill=True, levels=5, thresh=0.1)

# Joint plot with marginals
sns.jointplot(data=df, x='total_bill', y='tip',
              kind='scatter', hue='time')

# Pairwise relationships
sns.pairplot(data=df, hue='species', corner=True)

Categorical Plots (Comparisons Across Categories)

Use for: Comparing distributions or statistics across discrete categories

Categorical scatterplots:

• stripplot() - Points with jitter to show all observations
• swarmplot() - Non-overlapping points (beeswarm algorithm)

Distribution comparisons:

• boxplot() - Quartiles and outliers
• violinplot() - KDE + quartile information
• boxenplot() - Enhanced boxplot for larger datasets

Statistical estimates:

• barplot() - Mean/aggregate with confidence intervals
• pointplot() - Point estimates with connecting lines
• countplot() - Count of observations per category

Figure-level:

• catplot() - Faceted categorical plots (set kind parameter)

Key parameters:

• x, y - Variables (one typically categorical)
• hue - Additional categorical grouping
• order, hue_order - Control category ordering
• dodge - Separate hue levels side-by-side
• orient - "v" (vertical) or "h" (horizontal)
• kind - Plot type for catplot: "strip", "swarm", "box", "violin", "bar", "point"

# Swarm plot showing all points
sns.swarmplot(data=df, x='day', y='total_bill', hue='sex')

# Violin plot with split for comparison
sns.violinplot(data=df, x='day', y='total_bill',
               hue='sex', split=True)

# Bar plot with error bars
sns.barplot(data=df, x='day', y='total_bill',
            hue='sex', estimator='mean', errorbar='ci')

# Faceted categorical plot
sns.catplot(data=df, x='day', y='total_bill',
            col='time', kind='box')

Regression Plots (Linear Relationships)

Use for: Visualizing linear regressions and residuals

• regplot() - Axes-level regression plot with scatter + fit line
• lmplot() - Figure-level with faceting support
• residplot() - Residual plot for assessing model fit

Key parameters:

• x, y - Variables to regress
• order - Polynomial regression order
• logistic - Fit logistic regression
• robust - Use robust regression (less sensitive to outliers)
• ci - Confidence interval width (default 95)
• scatter_kws, line_kws - Customize scatter and line properties

# Simple linear regression
sns.regplot(data=df, x='total_bill', y='tip')

# Polynomial regression with faceting
sns.lmplot(data=df, x='total_bill', y='tip',
           col='time', order=2, ci=95)

# Check residuals
sns.residplot(data=df, x='total_bill', y='tip')

Matrix Plots (Rectangular Data)

Use for: Visualizing matrices, correlations, and grid-structured data

• heatmap() - Color-encoded matrix with annotations
• clustermap() - Hierarchically-clustered heatmap

Key parameters:

• data - 2D rectangular dataset (DataFrame or array)
• annot - Display values in cells
• fmt - Format string for annotations (e.g., ".2f")
• cmap - Colormap name
• center - Value at colormap center (for diverging colormaps)
• vmin, vmax - Color scale limits
• square - Force square cells
• linewidths - Gap between cells

# Correlation heatmap
corr = df.corr()
sns.heatmap(corr, annot=True, fmt='.2f',
            cmap='coolwarm', center=0, square=True)

# Clustered heatmap
sns.clustermap(data, cmap='viridis',
               standard_scale=1, figsize=(10, 10))

Multi-Plot Grids

Seaborn provides grid objects for creating complex multi-panel figures:

FacetGrid

Create subplots based on categorical variables. Most useful when called through figure-level functions (relplot, displot, catplot), but can be used directly for custom plots.

g = sns.FacetGrid(df, col='time', row='sex', hue='smoker')
g.map(sns.scatterplot, 'total_bill', 'tip')
g.add_legend()

PairGrid

Show pairwise relationships between all variables in a dataset.

g = sns.PairGrid(df, hue='species')
g.map_upper(sns.scatterplot)
g.map_lower(sns.kdeplot)
g.map_diag(sns.histplot)
g.add_legend()

JointGrid

Combine bivariate plot with marginal distributions.

g = sns.JointGrid(data=df, x='total_bill', y='tip')
g.plot_joint(sns.scatterplot)
g.plot_marginals(sns.histplot)

Figure-Level vs Axes-Level Functions

Understanding this distinction is crucial for effective seaborn usage:

Axes-Level Functions

• Plot to a single matplotlib Axes object
• Integrate easily into complex matplotlib figures
• Accept ax= parameter for precise placement
• Return Axes object
• Examples: scatterplot, histplot, boxplot, regplot, heatmap

When to use:

• Building custom multi-plot layouts
• Combining different plot types
• Need matplotlib-level control
• Integrating with existing matplotlib code

fig, axes = plt.subplots(2, 2, figsize=(10, 10))
sns.scatterplot(data=df, x='x', y='y', ax=axes[0, 0])
sns.histplot(data=df, x='x', ax=axes[0, 1])
sns.boxplot(data=df, x='cat', y='y', ax=axes[1, 0])
sns.kdeplot(data=df, x='x', y='y', ax=axes[1, 1])