LOWESS-Smoother-Implementation

Implementation of LOWESS (Locally Weighted Scatterplot Smoothing) algorithm with bootstrap confidence intervals for nonparametric regression and data smoothing in Python.

Overview

LOWESS is a powerful nonparametric technique proposed by Cleveland (1979) for modeling and smoothing two-dimensional data. This method is particularly useful for:

• Data smoothing - Extracting trends from noisy data
• Outlier detection - Identifying anomalies relative to local trends
• Forecasting - Building flexible regression models for volatile data
• Seasonal analysis - Handling periodic and evolutionary data series

Features

• LOWESS smoothing with customizable bandwidth
• Bootstrap confidence intervals (95% CI)
• Nonlinear data handling - perfect for cosine-like patterns
• Interactive visualization with matplotlib and seaborn
• Statistical robustness - resistant to outliers

Installation

# Clone repository
git clone https://github.com/esosetrov/LOWESS-Smoother-Implementation.git
cd LOWESS-Smoother-Implementation

Install dependencies

pip install numpy matplotlib seaborn statsmodels pandas

Usage

import numpy as np
import statsmodels.api as sm

# Generate sample data
x = np.random.uniform(0, 4 * np.pi, size=200)
y = np.cos(x) + np.random.random(size=len(x))

# Apply LOWESS smoothing
smoothed = sm.nonparametric.lowess(exog=x, endog=y, frac=0.2)

# Compute confidence intervals
from lowess_bootstrap import lowess_with_confidence_bounds
eval_x = np.linspace(0, 4 * np.pi, 31)
smoothed, bottom, top = lowess_with_confidence_bounds(
    x, y, eval_x, lowess_kw={"frac": 0.1}
)

Results

The implementation demonstrates:

• Smooth curve fitting through noisy data
• 95% confidence intervals via bootstrap resampling
• Effective handling of nonlinear patterns
• Robust performance in presence of outliers

Algorithm Details

LOWESS works by:

• Local fitting - Estimating each point using its neighbors
• Weighted regression - Using tricube weighting function
• Iterative refinement - Downweighting outliers in subsequent iterations
• Bootstrap validation - Assessing uncertainty through resampling

Applications

• Genetics research - Gene expression data analysis
• Financial modeling - Time series smoothing
• Signal processing - Noise reduction
• Quality control - Trend detection in manufacturing
• Environmental science - Climate data analysis

Project Structure

LOWESS-Smoother-Implementation/
├── lowess-smoother-algorithm.ipynb
├── README.md
├── LICENSE
├── .gitignore
└── requirements.txt

Dependencies

• Python 3.10+;
• numpy;
• matplotlib;
• seaborn;
• statsmodels;
• pandas;

Contributing

Contributions are welcome! Please feel free to submit a Pull Request.

License

This project is licensed under the MIT License - see the LICENSE file for details.

References

Cleveland, William S. (1979). "Robust Locally Weighted Regression and Smoothing Scatterplots". Journal of the American Statistical Association. Statsmodels Documentation: https://www.statsmodels.org Harrell, Frank E. Jr. "Regression Modeling Strategies" https://www.kaggle.com/code/eugeniyosetrov/lowess-smoother-algorithm

Note:

This notebook is designed for educational and research purposes. Real-world applications may require additional considerations and validation.