seaborn — quality + safety report

---
name: seaborn
description: Statistical visualization with pandas integration. Use for quick exploration of distributions, relationships, and categorical comparisons with attractive defaults. Best for box plots, violin plots, pair plots, heatmaps. Built on matplotlib. For interactive plots use plotly; for publication styling use scientific-visualization.
license: BSD-3-Clause license
metadata:
  version: "1.0"
  skill-author: K-Dense Inc.
---

# 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

```python
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

```python
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)

```python
# 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"

```python
# 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"

```python
# 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

```python
# 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

```python
# 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.

```python
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.

```python
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.

```python
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

```python
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])
```

### Figure-Level Functions
- Manage entire figure including all subplots
- Built-in faceting via `col` and `row` parameters
- Return `FacetGrid`, `JointGrid`, or `PairGrid` objects
- Use `height` and `aspect` for sizing (per subplot)
- Cannot be placed in existing figure
- Examples: `relplot`, `displot`, `catplot`, `lmplot`, `jointplot`, `pairplot`

**When to use:**
- Faceted visualizations (small multiples)
- Quick exploratory analysis
- Consistent multi-panel layouts
- Don't need to combine with other plot types

```python
# Automatic faceting
sns.relplot(data=df, x='x', y='y', col='category', row='group',
            hue='type', height=3, aspect=1.2)
```

## Data Structure Requirements

### Long-Form Data (Preferred)

Each variable is a column, each observation is a row. This "tidy" format provides maximum flexibility:

```python
# Long-form structure
   subject  condition  measurement
0        1    control         10.5
1        1  treatment         12.3
2        2    control          9.8
3        2  treatment         13.1
```

**Advantages:**
- Works with all seaborn functions
- Easy to remap variables to visual properties
- Supports arbitrary complexity
- Natural for DataFrame operations

### Wide-Form Data

Variables are spread across columns. Useful for simple rectangular data:

```python
# Wide-form structure
   control  treatment
0     10.5       12.3
1      9.8       13.1
```

**Use cases:**
- Simple time series
- Correlation matrices
- Heatmaps
- Quick plots of array data

**Converting wide to long:**
```python
df_long = df.melt(var_name='condition', value_name='measurement')
```

## Color Palettes

Seaborn provides carefully designed color palettes for different data types:

### Qualitative Palettes (Categorical Data)

Distinguish categories through hue variation:
- `"deep"` - Default, vivid colors
- `"muted"` - Softer, less saturated
- `"pastel"` - Light, desaturated
- `"bright"` - Highly saturated
- `"dark"` - Dark values
- `"colorblind"` - Safe for color vision d

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