Data Preprocessing in Machine Learning: 7 Key Steps to Follow, Strategies, & Applications
By Kechit Goyal
Updated on Jun 02, 2025 | 20 min read | 160.51K+ views
Share:
For working professionals
For fresh graduates
More
By Kechit Goyal
Updated on Jun 02, 2025 | 20 min read | 160.51K+ views
Share:
Table of Contents
Did you know that 59% of large companies in India have adopted machine learning solutions in their business processes? This shift highlights the growing demand for efficient data preprocessing in machine learning to ensure accurate, scalable, and production-ready model deployment.
Efficient model development starts with data preprocessing in machine learning, where raw data is cleaned, scaled, and encoded to ensure algorithmic compatibility and training stability. Techniques like imputation, normalization, and encoding reduce variance and bias during model training.
These steps form the core of reproducible, production-grade ML pipelines across domains. Accurate preprocessing is fundamental to real-time inference, optimization, and machine learning model performance.
In this blog, we will explore the steps of data preprocessing in machine learning along with strategies and practical applications.
Want to strengthen your machine learning skills for effective data processing and analysis? upGrad’s Artificial Intelligence & Machine Learning - AI ML Courses can equip you with tools and strategies to stay ahead. Enroll today!
Data preprocessing in machine learning is the process of converting messy, inconsistent, or incomplete raw data into a format that machine learning models can interpret effectively. It's a critical precursor to tasks like model training, evaluation, and data mining, where unprocessed data can distort insights and undermine results.
By resolving issues such as missing values, inconsistent formats, and redundant or noisy entries, preprocessing builds the foundation for reliable models and enables downstream processes.
If you want to learn machine learning skills for modern data-driven operations, the following courses from upGrad can help you succeed.
Let’s explore some of the major operations that are involved with data preprocessing in machine learning.
Before you can build reliable machine learning models, your raw data must be transformed into a structured format suitable for algorithmic consumption. This process data preprocessing in machine learning, involves multiple tasks designed to enhance data integrity, compatibility, and efficiency.
These steps are critical whether you're working with structured customer records, web interaction logs, or multi-source sensor data.
Let’s walk through the most essential ones.
As the first step in data preprocessing in machine learning, data cleaning removes inconsistencies, null entries, and irrelevant noise from raw input. Without this step, models trained on malformed data, like missing HTML form values or inconsistent TypeScript logs, produce skewed or unreliable outputs.
Tasks
Techniques
Example Scenario:
If you analyze frontend performance metrics from a TypeScript-based dashboard, cleaning null page-load times and duplicate session entries ensures stable input for churn prediction models. This step strengthens the data preprocessing in machine learning pipeline by minimizing noise and preserving signal integrity.
In data preprocessing in machine learning, integration combines datasets from different sources, like SQL databases, REST APIs, and Excel exports, into a unified schema. It resolves structural mismatches and ensures consistency across platforms before model training.
Tasks:
Techniques:
Example Scenario:
Integration resolves naming conflicts and field mismatches if you're consolidating product inventory from an ERP system and frontend metadata from a CSS-tagged HTML catalog. This ensures your data preprocessing in machine learning pipeline receives normalized inputs ready for clustering or recommendation models.
This stage adapts integrated data to model-friendly formats scaling numeric values, encoding categories, and smoothing distributions. Transformation enhances the compatibility of diverse data types for model convergence and interpretability.
Tasks:
Techniques:
Example Scenario:
When preprocessing e-commerce browsing data, transforming the time_spent field using log normalization and encoding browser_type helps gradient boosting models learn without scale bias. This step ensures smoother data preprocessing in machine learning, particularly for models sensitive to feature scaling.
Large datasets like telemetry logs from IoT or event streams in TypeScript apps can overwhelm memory and slow down training. Reduction eliminates non-essential variables while retaining predictive signals.
Tasks
Techniques
Example Scenario:
If you're working with clickstream data from a high-traffic Indian marketplace, reducing input dimensions using PCA improves model speed without sacrificing accuracy. This optimizes your data preprocessing in machine learning pipeline for efficient deployment on cloud environments.
Whether you're developing predictive models in Node.js for customer segmentation or working with Vue.js dashboards to visualize trends, the raw input data you receive is rarely clean. It often contains missing values, unaligned formats, and anomalies that degrade model accuracy.
Effective data preprocessing in machine learning transforms this fragmented input into a consistent, analyzable structure, bridging raw data and meaningful output.
Here are some of the key benefits of data preprocessing in machine learning:
Now, let’s explore some of the seven steps for effective data preprocessing in machine learning models.
Data preprocessing in machine learning is a structured sequence of steps designed to prepare raw datasets for modeling. These steps clean, transform, and format data, ensuring optimal performance for feature engineering in machine learning. Following these steps systematically enhances data quality and ensures model compatibility.
Here’s a step-by-step walkthrough of the data preprocessing workflow, using Python to illustrate key actions. For this process, we’re using the Titanic dataset from Kaggle.
To perform data preprocessing in machine learning, you must first import foundational libraries for data handling, numerical computation, and visualization. These libraries are crucial for building a structured preprocessing pipeline in Python.
Code Example:
|
Output:
|
Output Explanation:
All core libraries are now ready for use. This message confirms that your Python environment is configured properly to begin data preprocessing in machine learning using tools like pandas and numpy.
The Titanic dataset is loaded from a local file into a DataFrame, forming the baseline for all preprocessing activities.
Code Example:
|
Output:
|
Output Explanation:
You now have a 12-column dataset including features like Age, Fare, and Embarked. This serves as the raw input for data preprocessing in machine learning.
Before modifying the data, you must analyze the dataset’s structure to identify potential problems like missing values or skewed distributions.
Code Example:
|
Output:
|
Output Explanation:
You have 891 rows and 12 columns. Age, Cabin, and Embarked require special attention due to missing data.
Missing entries in your dataset can skew training and evaluation. You’ll address this by inputting or removing values based on context.
Code Example:
|
Output:
|
Output Explanation:
All missing values have been addressed. Your dataset is now complete and valid for further processing in your data preprocessing in machine learning pipeline.
ML models require numerical inputs. You’ll now convert text categories, like Sex and Embarked, into numerical formats.
Code Example:
|
Output:
|
Output Explanation:
Sex is now 0 or 1. Embarked has been transformed into two binary flags. These fields are now usable by most ML algorithms.
Unscaled numeric features can introduce bias, especially in distance-based or regularized models. Standardization ensures all values contribute proportionally.
Code Example:
|
Output:
|
Output Explanation:
Age and Fare are now centered at 0 with a standard deviation 1. This improves training dynamics for logistic regression, SVM, and k-means clustering.
Divide the data into training and testing subsets to evaluate performance accurately and avoid overfitting.
Code Example:
|
Output:
|
Output Explanation:
Your dataset is now partitioned for training and evaluation. The model will be trained on 712 samples and tested on 179 unseen samples, supporting data preprocessing in machine learning practices.
Before starting data preprocessing in machine learning, you must acquire a dataset aligned with your modeling objectives. Whether you're building a binary classifier or a regression model, the quality and structure of your data directly affect downstream processes like feature engineering and validation. Source reliability, file compatibility, and data relevance are critical at this stage.
For efficient data preprocessing in machine learning, Python offers specialized libraries tailored to handle various pipeline stages, ranging from array operations and structured data handling to exploratory visualization. These libraries ensure your preprocessing steps are reproducible, scalable, and aligned with standard machine learning practices.
Library | Purpose |
NumPy | Performs optimized numerical operations on arrays and matrices. Enables element-wise computations and supports linear algebra. |
Pandas | Provides powerful data structures like DataFrame for manipulating structured/tabular data. |
Matplotlib | Supports data visualization to explore feature distributions, trends, and outliers visually. |
Code Example:
|
Output:
|
Output Explanation:
This output confirms that your development environment is ready. With NumPy, Pandas, and Matplotlib available, you can begin structured data preprocessing in machine learning, including tasks like normalization, missing value handling, and plotting distributions.
Once you have acquired the dataset and imported the necessary libraries, the next step is to load the data into your workspace. This step ensures your data is ready for processing and analysis.
Below are the steps to load your dataset:
Example Code for Loading the Dataset
# Load the dataset
dataset = pd.read_csv('Dataset.csv')
# Extract independent and dependent variables
X = dataset.iloc[:, :-1].values # Features
y = dataset.iloc[:, -1].values # Target
Example output:
Step |
Output |
Load the Dataset | Displays the first few rows of the dataset. Example: pd.read_csv('Dataset.csv') shows columns like PassengerId, Survived, Age, Fare, etc. |
Independent Variables (X) | Extracted features. Example: 2D array with rows representing records and columns representing features like Age, Fare, Pclass. Example: [[22.0, 7.25], [38.0, 71.28]]. |
Dependent Variable (y) | Extracted target variable. Example: 1D array representing outcomes like [0, 1, 1, 0, 0, ...], such as the Survived column in the Titanic dataset. |
Once the data is loaded, the next step is to identify and address missing values to ensure completeness.
Detecting and addressing missing data is a critical step in data preprocessing in machine learning. Missing data, if left untreated, can lead to incorrect conclusions and flawed models. Ensuring data completeness improves the reliability of feature engineering in machine learning.
The following methods are commonly used to handle missing data.
Similar Read: Data Preprocessing In Data Mining: Steps, Missing Value Imputation, Data Standardization
Once missing data is addressed, the dataset is ready for further transformations like encoding categorical variables for machine learning models.
Machine learning algorithms require numerical inputs. Encoding categorical data into numerical form is an essential step in data preprocessing. It transforms categories into formats that algorithms can interpret effectively.
Below are the most commonly used techniques for encoding categorical variables.
Technique |
Description |
Label Encoding | Converts categories into numeric labels. Example: 'India', 'France' → 0, 1. |
Dummy Encoding (OneHot) | Converts categories into binary format with dummy variables. |
Code Examples for Label Encoding:
from sklearn.preprocessing import LabelEncoder
labelencoder = LabelEncoder()
dataset['Sex'] = labelencoder.fit_transform(dataset['Sex'])
Before Label Encoding |
After Label Encoding |
male | 1 |
female | 0 |
male | 1 |
Code Examples for Dummy Encoding:
dataset = pd.get_dummies(dataset, columns=['Embarked'], drop_first=True)
Before Dummy Encoding |
After Dummy Encoding |
S | Embarked_Q = 0, Embarked_S = 1 |
C | Embarked_Q = 0, Embarked_S = 0 |
Q | Embarked_Q = 1, Embarked_S = 0 |
After encoding categorical variables, the dataset becomes entirely numerical and ready for outlier management.
Outliers can significantly impact model predictions and skew results. Detecting and managing them ensures that your data is consistent and reliable for analysis.
The following techniques are widely used for outlier detection and handling.
Code Example for Outlier Detection and Handling
# Z-Score Method
from scipy.stats import zscore
z_scores = zscore(dataset['Fare'])
dataset = dataset[(z_scores < 3).all(axis=1)] # Remove rows where z-score exceeds 3
Step |
Output |
Before Outlier Removal | Fare column includes extreme values such as 512.33 or 263.00, significantly higher than the mean of 32.20. |
After Outlier Removal | Rows with extreme Fare values removed; dataset is now more consistent, with Fare values within a manageable range (e.g., 0 to ~150). |
Also Read: Types of Machine Learning Algorithms with Use Cases Examples
Addressing outliers paves the way for splitting the dataset and scaling features for optimal performance.
Splitting the dataset ensures a fair evaluation of model performance. Scaling features standardizes values, ensuring each feature contributes equally during training.
Splitting the Dataset
Typical split ratios are 70:30 or 80:20. The train_test_split() function in Python simplifies this process.
from sklearn.model_selection import train_test_split
X = dataset.drop(columns=['Survived'])
y = dataset['Survived']
X_train, X_test, y_train, y_test = train_test_split(X, y, test_size=0.2, random_state=42)
Step |
Output |
Training Set Shape (X) | (712, n) – Contains 80% of the dataset. |
Test Set Shape (X) | (179, n) – Contains 20% of the dataset. |
Scaling Features
Feature scaling ensures uniformity in data range. This step is vital for algorithms that depend on distance metrics.
from sklearn.preprocessing import StandardScaler
scaler = StandardScaler()
X_train_scaled = scaler.fit_transform(X_train)
X_test_scaled = scaler.transform(X_test)
Step |
Output |
Standardized Features (X_train_scaled) | Values have a mean of 0 and standard deviation of 1. Example: Age is now standardized to values like -0.5, 1.2. |
Standardized Features (X_test_scaled) | Scaled using the same mean and variance as the training set to ensure consistency. |
Now the dataset is fully preprocessed and ready for training machine learning models. This sets the stage for understanding how to handle imbalanced datasets effectively.
In production environments, whether you're predicting fraudulent transactions from REST API logs or diagnosing rare conditions from clinical MongoDB records, imbalanced datasets in machine learning are a frequent obstacle.
When one class dominates, models tend to be biased toward it, misclassifying rare but significant events. Addressing this imbalance is critical for fraud detection, anomaly detection, customer retention, and medical diagnostics applications.
Below are proven approaches to improve model reliability across skewed class distributions.
1. Resampling Techniques
2. Synthetic Data Generation
3. Cost-Sensitive Learning
4. Ensemble Methods
Aslo Read: Top Python Libraries for Machine Learning for Efficient Model Development in 2025
Imbalanced datasets pose significant challenges, but these approaches ensure fair representation and improved model performance. The next section explores how data preprocessing and feature engineering drive model performance in machine learning.
The success of any predictive model doesn’t start with algorithms; it begins with how well your data is prepared and represented. Through structured data preprocessing in machine learning, followed by targeted feature engineering, you ensure that input data reflects the right patterns and relationships for learning.
These techniques transform raw variables into meaningful signals, enhancing accuracy, reducing overfitting, and improving generalization on unseen data.
Here’s how data preprocessing and feature engineering drive model performance:
Use Case:
In a fraud detection system built on transactional REST API data, applying data preprocessing in machine learning, including scaling amounts and encoding transaction types. These engineered features allowed gradient boosting models to identify rare fraud cases without increasing false positives.
Also read: Top 5 Machine Learning Models Explained For Beginners
Moving forward, the next section examines the role of data preprocessing in various machine-learning applications.
In practical systems, from recommendation engines to fraud detection, data preprocessing in machine learning is a foundational layer that enables intelligent automation, accuracy, and scalability. Beyond cleaning and transformation, preprocessing supports practical feature engineering, ensures input consistency, and streamlines the entire ML lifecycle.
Below are examples illustrating how data preprocessing contributes to practical applications in machine learning and AI.
Application | Description |
Core Elements of AI and ML Development | Preprocessing delivers clean, consistent input, improving algorithmic stability and model precision. |
Reusable Building Blocks for Innovation | Scaled and encoded datasets enable iterative modeling and serve as reusable assets across pipelines. |
Streamlining Business Intelligence | Helps uncover trends, outliers, and patterns that drive data-driven decisions in Power BI dashboards. |
Improving CRM through Web Mining | Structured session and interaction logs allow CRM tools to personalize recommendations and content. |
Personalized Insights from Session Data | Identifies user behavior, preferences, and intent from web logs or tracking pixels. |
Driving Accuracy in Consumer Research | Ensures valid, noise-free inputs for customer segmentation and product design insights. |
If you are interested in learning the basics of data visualization, check out upGrad’s Case Study using Tableau, Python and SQL. The 10-hour free program will help you gain expertise on creating dashboards and analyzing churn rates for enterprise-grade applications.
Let’s explore the top strategies for effective data preprocessing and feature engineering in machine learning.
In production-ready ML systems, whether deployed via Docker, orchestrated through Jenkins, or hosted on AWS, your pipeline is only as good as the data you feed it. Efficient data preprocessing and feature engineering in machine learning transform raw input into structured, signal-rich formats that drive model accuracy. These strategies are essential for teams integrating ML with DevOps workflows, CI/CD pipelines, or scalable cloud architectures.
Example Scenario:
Suppose you're building a predictive maintenance model using sensor data from delivery vehicles streamed via REST APIs. After imputing missing values and reducing dimensionality with PCA, you engineer a new feature, fuel consumption per delivery, which improves model recall by 18%. The entire data preprocessing and feature engineering in the machine learning pipeline is automated using Docker and Jenkins for real-time deployment on AWS.
If you want to gain expertise in machine learning with cloud computing, check out upGrad’s Professional Certificate Program in Cloud Computing and DevOps. The program will help you build the core principles of DevOps, AWS, GCP, and more.
The next section delves into transformative applications of data processing in machine learning and its role in driving business outcomes.
Data preprocessing in machine learning and feature engineering in machine learning are driving innovations across industries. They enable businesses to derive actionable insights, enhance decision-making, and deliver personalized customer experiences.
The applications span various domains, showcasing how effective data handling impacts both operational efficiency and strategic growth.
Application |
Description |
Customer Segmentation | Data preprocessing helps group customers based on behaviors and preferences, enabling targeted marketing strategies. |
Predictive Maintenance | Feature engineering identifies patterns in sensor data to predict equipment failures, reducing downtime. |
Fraud Detection | Machine learning models trained on preprocessed transaction data detect anomalies and fraudulent activities effectively. |
Healthcare Diagnosis | Clean and structured medical data supports accurate disease detection and personalized treatment recommendations. |
Supply Chain Optimization | Feature engineering optimizes logistics by forecasting demand and minimizing inefficiencies. |
Recommendation Systems | Preprocessed user data improves recommendation engines for e-commerce and streaming platforms, boosting engagement. |
Sentiment Analysis | Text preprocessing enables sentiment classification, helping brands analyze public perception and customer feedback. |
Next, the focus shifts to how upGrad can enhance your data processing and machine learning expertise to advance your career and technical skills.
Structured data pipelines begin with rigorous preprocessing, covering missing value treatment, normalization, encoding, and dimensionality reduction, to stabilize learning and improve model accuracy. These steps support applications like fraud detection, predictive maintenance, and personalization by enhancing data integrity and feature relevance.
Use tools like Scikit-learn, Jenkins, and Docker to automate your data preprocessing in machine learning for scalable, production-ready deployment.
If you want to learn industry-relevant machine learning skills for data processing and analysis. These are some of the additional courses from upGrad that can help you succeed.
Curious which courses can help you in machine learning? Contact upGrad for personalized counseling and valuable insights. For more details, you can also visit your nearest upGrad offline center.
Expand your expertise with the best resources available. Browse the programs below to find your ideal fit in Best Machine Learning and AI Courses Online.
Discover in-demand Machine Learning skills to expand your expertise. Explore the programs below to find the perfect fit for your goals.
Discover popular AI and ML blogs and free courses to deepen your expertise. Explore the programs below to find your perfect fit.
Dataset:
Titanic: https://www.kaggle.com/c/titanic/data
Reference:
https://www.itransition.com/machine-learning/statistics
95 articles published
Experienced Developer, Team Player and a Leader with a demonstrated history of working in startups. Strong engineering professional with a Bachelor of Technology (BTech) focused in Computer Science fr...
Get Free Consultation
By submitting, I accept the T&C and
Privacy Policy
Top Resources