How Do You Handle Missing or Corrupted Data in a Dataset?
In the world of machine learning, data is the foundation upon which models are built. However, real-world datasets are rarely perfect. They often contain missing or corrupted data due to various reasons such as human errors, system glitches, or incomplete data collection processes. Handling such data effectively is crucial because poor data quality can lead to inaccurate models, misleading insights, and unreliable predictions. Whether you're enrolled in machine learning classes in Pune or exploring advanced techniques in data science, understanding how to manage missing or corrupted data is an essential skill.


This blog delves into the best practices for handling missing and corrupted data, ensuring that your machine learning models remain robust and accurate.


What Causes Missing or Corrupted Data?
Before exploring solutions, it’s important to understand why data issues occur:


Human Error: Mistakes during data entry or manual handling can result in missing values.
Data Collection Issues: Incomplete surveys, sensor malfunctions, or transmission errors can cause gaps.
System Failures: Software bugs, hardware malfunctions, or network interruptions can corrupt data.
Data Integration Problems: Merging datasets from different sources without proper alignment can lead to inconsistencies.
Understanding the root cause helps determine the most appropriate method for handling the problem.


Types of Missing Data
Missing data can be categorized into three types:


Missing Completely at Random (MCAR): The missingness is entirely random and not related to any other data. For example, a sensor occasionally fails without any identifiable pattern.
Missing at Random (MAR): The missingness is related to other observed data but not the missing data itself. For example, older respondents in a survey might be less likely to answer questions about technology usage.
Missing Not at Random (MNAR): The missingness is related to the missing data itself. For example, people with higher incomes may choose not to disclose their income levels in surveys.
Identifying the type of missing data helps in choosing the right handling technique.


Techniques to Handle Missing Data
1. Deletion Methods
Listwise Deletion: Removes entire rows where any data is missing. This is simple but can result in significant data loss if many records have missing values.
Pairwise Deletion: Analyzes data only with available values for each specific analysis. This retains more data but can complicate correlation calculations.
When to Use: Deletion methods are suitable when the dataset is large, and missing data is minimal and random (MCAR).


2. Imputation Techniques
Imputation involves filling in missing values with substitute data.


Mean/Median/Mode Imputation: Replaces missing values with the mean (for continuous data), median (for skewed data), or mode (for categorical data).
K-Nearest Neighbors (KNN) Imputation: Estimates missing values based on the values of similar (neighboring) data points.
Regression Imputation: Uses regression models to predict missing values based on other features.
Multiple Imputation: Generates multiple datasets with imputed values and averages the results, accounting for uncertainty in missing data.
When to Use: Imputation is effective when missing data is MAR and you want to retain as much information as possible without biasing the dataset.


3. Using Algorithms That Handle Missing Data Natively
Some machine learning algorithms, like decision trees and XGBoost, can handle missing values internally without requiring preprocessing.


When to Use: Ideal when working with large datasets where imputation may be resource-intensive.


Handling Corrupted Data
Corrupted data includes inaccurate, inconsistent, or outlier values that don’t make logical sense.


1. Identifying Corrupted Data
Data Profiling: Analyze datasets to detect anomalies or inconsistencies.
Validation Rules: Apply business rules or data constraints (e.g., age should be between 0 and 12.
Outlier Detection: Use statistical methods like Z-scores or machine learning techniques like Isolation Forests to identify abnormal data points.
2. Correcting or Removing Corrupted Data
Data Cleaning: Manually correct errors when feasible, especially in small datasets.
Standardization: Ensure consistent data formats (e.g., date formats, units of measurement).
Outlier Treatment: Depending on the context, outliers can be corrected, transformed, or removed.
When to Use: Apply correction methods when data can be verified, and removal methods when errors cannot be confidently corrected. Visit- https://www.sevenmentor.com/da....ta-analytics-courses