Machine Learning Lifecycle

A beginner-friendly guide to the stages involved in a machine learning project.

The lifecycle of a machine learning project involves a series of well-defined stages, each critical for developing successful models. This guide outlines these stages in simple terms and provides insights into best practices for each step. Additionally, we will introduce CRISP-DM, a popular methodology used in data science projects.

CRISP-DM Overview

CRISP-DM stands for Cross-Industry Standard Process for Data Mining. It's a widely-used framework that helps guide data science projects through a sequence of steps. The main phases of CRISP-DM are:

  1. Business Understanding
  2. Data Understanding
  3. Data Preparation
  4. Modeling
  5. Evaluation
  6. Deployment

We'll use this framework to structure our discussion of the machine learning lifecycle.

1. Business Understanding

The first step in any machine learning project is to clearly define the problem you aim to solve. This involves understanding the business context, identifying the key objectives, and determining the success criteria.

"A problem well stated is a problem half-solved." — Charles Kettering


Suppose a company wants to predict whether customers will buy a product based on their browsing history. The goal is to increase sales by targeting customers who are likely to buy.

2. Data Collection (Data Understanding)

Collecting data is a crucial step that lays the foundation for your project. Data can come from various sources such as databases, APIs, or web scraping.

  • Identify data sources: Determine where your data will come from.
  • Collect data: Use appropriate tools and techniques to gather the required data.
  • Store data: Ensure the data is stored securely and in a structured format.


The company collects data on customer browsing history, past purchases, and demographic information.

3. Data Cleaning (Data Preparation)

Raw data often contains noise and inconsistencies. Cleaning the data involves handling missing values, removing duplicates, and correcting errors to ensure high-quality input for your models.

# Example of data cleaning using Python
import pandas as pd

# Load data
data = pd.read_csv('data.csv')

# Remove duplicates

# Fill missing values
data.fillna(method='ffill', inplace=True)


The company removes duplicate entries and fills in missing values for customer age and gender.

4. Exploratory Data Analysis (EDA) (Data Preparation)

EDA involves analyzing the data to uncover patterns, trends, and relationships. This step helps in understanding the data distribution and identifying potential features for the model.

  • Visualize data: Use plots and graphs to get insights into the data.
  • Summary statistics: Calculate mean, median, standard deviation, etc.
  • Feature engineering: Create new features that might improve model performance.


The company visualizes the distribution of customer ages and finds that younger customers are more likely to browse frequently.

5. Data Preprocessing (Data Preparation)

Data preprocessing involves transforming the data into a format suitable for training machine learning models. This may include scaling, normalization, and encoding categorical variables.

# Example of data preprocessing
from sklearn.preprocessing import StandardScaler, OneHotEncoder
from sklearn.compose import ColumnTransformer

# Define the preprocessing steps
preprocessor = ColumnTransformer(
        ('num', StandardScaler(), numerical_features),
        ('cat', OneHotEncoder(), categorical_features)

# Apply the transformations
data_preprocessed = preprocessor.fit_transform(data)


The company scales numerical features like browsing time and encodes categorical features like gender.

6. Model Selection (Modeling)

Selecting the right model is critical for achieving good performance. Consider various algorithms and evaluate them based on your problem and data characteristics.

  • Algorithm selection: Choose appropriate algorithms for your task (e.g., regression, classification).
  • Baseline model: Start with a simple model to set a performance baseline.
  • Model comparison: Compare different models using cross-validation.


The company tries different algorithms like logistic regression and decision trees to see which works best for predicting purchases.

7. Model Training (Modeling)

Train the selected model using your training data. This step involves feeding the data into the model and adjusting its parameters to minimize errors.

# Example of model training
from sklearn.model_selection import train_test_split
from sklearn.linear_model import LogisticRegression

# Split data into training and testing sets
X_train, X_test, y_train, y_test = train_test_split(X, y, test_size=0.2, random_state=42)

# Train the model
model = LogisticRegression(), y_train)


The company trains a logistic regression model using 80% of the data and keeps 20% for testing.

8. Model Evaluation (Evaluation)

Evaluate the trained model using your testing data to assess its performance. Use appropriate metrics depending on the problem type (e.g., accuracy, precision, recall, RMSE).

  • Performance metrics: Calculate relevant metrics to evaluate model performance.
  • Validation: Validate the model using cross-validation techniques.
  • Error analysis: Analyze the errors to identify areas for improvement.


The company evaluates the model using accuracy and recall to ensure it correctly identifies customers who will make a purchase.

9. Model Deployment (Deployment)

Once the model is evaluated and fine-tuned, it is ready for deployment. This involves integrating the model into a production environment where it can make predictions on new data.

  • Model serving: Deploy the model using APIs, microservices, or cloud platforms.
  • Monitoring: Continuously monitor the model's performance in production.
  • Maintenance: Update and retrain the model as needed to ensure its accuracy over time.


The company deploys the model on their website to recommend products to customers in real-time.

10. Model Maintenance (Deployment)

The final stage involves maintaining the model by monitoring its performance and retraining it with new data to ensure it remains accurate and relevant.

  • Continuous monitoring: Keep track of model performance metrics.
  • Retraining: Regularly update the model with new data.
  • Feedback loop: Use feedback to improve the model iteratively.


The company continuously monitors the model's performance and retrains it every month with the latest customer data.


The machine learning lifecycle is a structured approach to developing and deploying machine learning models. By following these stages diligently and understanding the CRISP-DM methodology, you can ensure the success and reliability of your machine learning projects.