seaborn-statistical-visualization

# Seaborn — Statistical Visualization

## Overview

Seaborn is a Python visualization library for creating publication-quality statistical graphics with minimal code. It works directly with pandas DataFrames, provides automatic statistical estimation (means, CIs, KDE), and offers attractive default themes. Built on matplotlib for full customization access.

## When to Use

- Creating distribution plots (histograms, KDE, violin plots, box plots) for data exploration
- Visualizing relationships between variables with automatic trend fitting and confidence intervals
- Comparing distributions across categorical groups (treatment vs control, tissue types)
- Generating correlation heatmaps and clustered heatmaps
- Quick exploratory data analysis with `pairplot` for all pairwise relationships
- Multi-panel figures with automatic faceting by categorical variables
- For **interactive plots** with hover/zoom, use plotly instead
- For **low-level figure control** or custom layouts, use matplotlib directly

## Prerequisites

```bash
pip install seaborn matplotlib pandas
```

## Quick Start

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

df = sns.load_dataset("tips")
sns.scatterplot(data=df, x="total_bill", y="tip", hue="day", style="time")
plt.title("Tips by Day and Time")
plt.tight_layout()
plt.savefig("scatter.png", dpi=150)
print("Saved scatter.png")
```

## Core API

### 1. Distribution Plots

Visualize univariate and bivariate distributions.

```python
import seaborn as sns
import matplotlib.pyplot as plt

df = sns.load_dataset("tips")

# Histogram with density normalization
fig, axes = plt.subplots(1, 3, figsize=(15, 4))

sns.histplot(data=df, x="total_bill", hue="time", stat="density",
             multiple="stack", ax=axes[0])
axes[0].set_title("Histogram")

# KDE (smooth density estimate)
sns.kdeplot(data=df, x="total_bill", hue="time", fill=True,
            bw_adjust=0.8, ax=axes[1])
axes[1].set_title("KDE")

# ECDF (empirical cumulative distribution)
sns.ecdfplot(data=df, x="total_bill", hue="time", ax=axes[2])
axes[2].set_title("ECDF")

plt.tight_layout()
plt.savefig("distributions.png", dpi=150)
print("Saved distributions.png")
```

```python
# Bivariate KDE with contours
sns.kdeplot(data=df, x="total_bill", y="tip", fill=True,
            levels=5, thresh=0.1, cmap="mako")
plt.title("Bivariate KDE")
plt.savefig("bivariate_kde.png", dpi=150)
```

### 2. Categorical Plots

Compare distributions or estimates across discrete categories.

```python
import seaborn as sns
import matplotlib.pyplot as plt

df = sns.load_dataset("tips")
fig, axes = plt.subplots(1, 3, figsize=(15, 4))

# Box plot — quartiles and outliers
sns.boxplot(data=df, x="day", y="total_bill", hue="sex",
            dodge=True, ax=axes[0])
axes[0].set_title("Box Plot")

# Violin plot — KDE + quartiles
sns.violinplot(data=df, x="day", y="total_bill", hue="sex",
               split=True, inner="quart", ax=axes[1])
axes[1].set_title("Violin Plot")

# Bar plot — mean with CI
sns.barplot(data=df, x="day", y="total_bill", hue="sex",
            estimator="mean", errorbar="ci", ax=axes[2])
axes[2].set_title("Bar Plot (mean ± 95% CI)")

plt.tight_layout()
plt.savefig("categorical.png", dpi=150)
print("Saved categorical.png")
```

```python
# Swarm plot — all individual observations, non-overlapping
sns.swarmplot(data=df, x="day", y="total_bill", hue="sex", dodge=True)
plt.title("Swarm Plot")
plt.savefig("swarm.png", dpi=150)
```

### 3. Relational Plots

Explore relationships between continuous variables.

```python
import seaborn as sns
import matplotlib.pyplot as plt

df = sns.load_dataset("tips")

# Scatter with multiple semantic mappings
sns.scatterplot(data=df, x="total_bill", y="tip",
                hue="day", size="size", style="time")
plt.title("Scatter with Multi-Encoding")
plt.savefig("relational.png", dpi=150)
```

```python
# Line plot with automatic aggregation and CI
fmri = sns.load_dataset("fmri")
sns.lineplot(data=fmri, x="timepoint", y="signal",
             hue="region", style="event", errorbar="sd")
plt.title("Line Plot (mean ± SD)")
plt.savefig("lineplot.png", dpi=150)
```

### 4. Regression Plots

Fit and visualize linear models.

```python
import seaborn as sns
import matplotlib.pyplot as plt

df = sns.load_dataset("tips")

fig, axes = plt.subplots(1, 2, figsize=(12, 4))

# Linear regression with CI band
sns.regplot(data=df, x="total_bill", y="tip", ci=95, ax=axes[0])
axes[0].set_title("Linear Regression")

# Residual plot (check model assumptions)
sns.residplot(data=df, x="total_bill", y="tip", ax=axes[1])
axes[1].set_title("Residuals")

plt.tight_layout()
plt.savefig("regression.png", dpi=150)
print("Saved regression.png")
```

### 5. Matrix Plots

Visualize rectangular data (correlations, heatmaps).

```python
import seaborn as sns
import matplotlib.pyplot as plt
import numpy as np

# Correlation heatmap
df = sns.load_dataset("tips")
corr = df.select_dtypes(include=[np.number]).corr()

sns.heatmap(corr, annot=True, fmt=".2f", cmap="coolwarm",
            center=0, square=True, linewidths=0.5)
plt.title("Correlation Heatmap")
plt.tight_layout()
plt.savefig("heatmap.png", dpi=150)
print("Saved heatmap.png")
```

```python
# Clustered heatmap with hierarchical clustering
flights = sns.load_dataset("flights").pivot(index="month", columns="year", values="passengers")
sns.clustermap(flights, cmap="viridis", standard_scale=1,
               figsize=(10, 8), linewidths=0.5)
plt.savefig("clustermap.png", dpi=150)
```

### 6. Figure-Level Functions and Faceting

Create multi-panel figures with automatic faceting.

```python
import seaborn as sns

df = sns.load_dataset("tips")

# relplot — faceted scatter/line plots
g = sns.relplot(data=df, x="total_bill", y="tip",
                col="time", row="sex", hue="smoker",
                kind="scatter", height=3, aspect=1.2)
g.set_axis_labels("Total Bill ($)", "Tip ($)")
g.savefig("faceted_scatter.png", dpi=150)
print("Saved facete