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Machine Learning Notes

Algorithms, math, Python and real ML projects — written by CodingNow 2.0's mentors. Free to read, structured to actually help you learn.

Machine Learning notes by CodingNow 2.0 cover 247 topics — from what is machine learning? to ml ci/cd — each explained with short definitions, syntax and runnable code examples. They are 100% free, need no signup, and work as quick revision for college exams, Machine Learning interviews and CodingNow 2.0's mentor-led Machine Learning course in Pitampura, Delhi.

ML Fundamentals

What machine learning actually is, how it differs from AI/DL/Data Science, and the ML project lifecycle.

Beginner~3.5 hrs
14 topics

Python for ML

NumPy, Pandas, Matplotlib and scikit-learn — only the parts you actually need for ML.

Beginner~3 hrs
10 topics

Mathematics for ML

Linear algebra, calculus and probability — explained with intuition first, formulas second.

Beginner–Intermediate~5 hrs
20 topics

Statistics for ML

Descriptive stats, distributions, correlation and hypothesis testing with practical ML examples.

Beginner–Intermediate~4 hrs
6 topics

Data Preprocessing

Cleaning, encoding and scaling data correctly — and avoiding data leakage.

Beginner–Intermediate~4 hrs
16 topics

Exploratory Data Analysis

Understanding a dataset before modeling it — univariate to multivariate analysis.

Beginner–Intermediate~2.5 hrs
7 topics

Feature Engineering

Creating, transforming and selecting the features that make models work.

Intermediate~4.5 hrs
15 topics

Linear Regression

The foundational regression algorithm — equation, cost function and gradient descent.

Beginner–Intermediate~2.5 hrs
9 topics

Logistic Regression

The baseline classification algorithm, built on the sigmoid function.

Beginner–Intermediate~2 hrs
7 topics

K-Nearest Neighbors

A simple, instance-based algorithm for classification and regression.

Beginner–Intermediate~2 hrs
8 topics

Decision Trees

Gini, entropy, information gain and pruning — how trees split and overfit.

Intermediate~2.5 hrs
9 topics

Random Forest

Bagged decision trees — why an ensemble usually beats a single tree.

Intermediate~2 hrs
7 topics

Support Vector Machines

Margins, support vectors and the kernel trick for linear and non-linear boundaries.

Intermediate~2.5 hrs
9 topics

Naive Bayes

Bayes' theorem applied to classification — fast, simple, surprisingly effective.

Intermediate~2 hrs
6 topics

Clustering & Unsupervised Learning

K-Means, hierarchical clustering and DBSCAN — finding structure without labels.

Intermediate~3 hrs
10 topics

Dimensionality Reduction

PCA, t-SNE and UMAP — compressing features while keeping signal.

Intermediate–Advanced~2.5 hrs
8 topics

Ensemble Learning

Bagging, boosting and stacking — XGBoost, LightGBM and CatBoost compared.

Intermediate–Advanced~3 hrs
11 topics

Model Evaluation

Confusion matrix, precision/recall/F1, ROC-AUC and regression error metrics.

Intermediate~3.5 hrs
19 topics

Overfitting & Regularization

Bias-variance tradeoff, L1/L2 regularization and early stopping.

Intermediate~2 hrs
9 topics

Hyperparameter Tuning

Grid search, random search and Bayesian optimization for model selection.

Intermediate~1.5 hrs
7 topics

Imbalanced Data

Why accuracy lies on imbalanced datasets, and how to fix it.

Intermediate~1.5 hrs
6 topics

ML Pipelines

scikit-learn Pipeline and ColumnTransformer — reproducible, leak-free workflows.

Intermediate~1.5 hrs
6 topics

Explainable ML

SHAP, LIME and permutation importance — interpretability vs explainability.

Advanced~2 hrs
6 topics

ML Model Deployment

Saving models and serving predictions with Flask, FastAPI, Streamlit and Docker.

Advanced~2.5 hrs
10 topics

MLOps Fundamentals

Versioning, experiment tracking, monitoring, drift and retraining.

Advanced~2.5 hrs
11 topics

ML System Design

Feature stores, online vs offline inference, and scaling ML systems.

Advanced~2 hrs
Coming Soon

ML Projects

End-to-end builds — EDA through deployment — on realistic datasets.

Intermediate–Advanced~6 hrs
Coming Soon

Interview Questions

Topic-wise ML interview questions with detailed, explained answers.

All levels~4 hrs
Coming Soon

Practice Questions

Implementation-oriented exercises across preprocessing, modeling and evaluation.

All levels~3 hrs
Coming Soon

Cheat Sheets

Concise reference pages for algorithms, metrics and scikit-learn syntax.

All levels~1 hr
Coming Soon

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ML Fundamentals

14 of 14 topics published
101

What Is Machine Learning?

A practical definition of ML, how it differs from traditional programming, and a working code example.

102

How Machine Learning Works

The represent-predict-measure-improve loop behind every ML algorithm, with a worked example.

103

Types of Machine Learning

Supervised, unsupervised, semi-supervised, self-supervised and reinforcement learning compared.

104

Supervised Learning

Regression vs classification, a full scikit-learn example, and when supervised learning applies.

105

Unsupervised Learning

Clustering and dimensionality reduction explained, with a K-Means customer segmentation example.

106

Semi-Supervised Learning

How self-training works, and when it beats collecting more labeled data.

107

Self-Supervised Learning

How models generate their own training labels from raw data, and why it powers modern LLMs.

108

Reinforcement Learning

The agent-environment-reward loop, and why reward design is the hardest part of RL.

109

Machine Learning vs AI

Why ML is a subset of AI, not a synonym for it, with a clear containment diagram.

110

Machine Learning vs Deep Learning

Feature engineering vs automatic feature learning, and when to choose each approach.

111

Machine Learning vs Data Science

Why data science is the broader discipline, and ML is one tool within it.

112

ML Workflow

The 10-step technical workflow from problem definition to monitoring, with a full code example.

113

ML Project Lifecycle

The 5-stage business-facing lifecycle that wraps around the technical ML workflow.

114

Common Machine Learning Problems

The recurring problem types — regression, classification, clustering, ranking and more — mapped to algorithms.

Mathematics for ML

20 of 21 topics published
301

Math for Machine Learning

The three math pillars behind ML — linear algebra, calculus and probability — and how deep you actually need to go.

309

Linear Algebra

The building blocks of linear algebra for ML — vectors, matrices, dot products — tied together.

302

Vectors

What a feature vector represents, vector addition geometrically, and the magnitude formula.

304

Matrices

Your dataset as a matrix, and how matrix-vector multiplication powers every linear model prediction.

310

Matrix Multiplication

The formula, a worked example, and why matrix multiplication order matters.

303

Dot Product

The formula, geometric projection intuition, and where the dot product shows up across ML algorithms.

311

Eigenvalues

The formula, characteristic equation, and a worked example solving for eigenvalues.

312

Eigenvectors

Solving for eigenvectors given an eigenvalue, and why PCA components are always orthogonal.

313

Vector Space

Basis, dimension and span — and how they explain feature space and redundant features.

314

Calculus for Machine Learning

Why calculus underlies model training, and how derivatives, gradients and the chain rule connect.

315

Derivatives

The formal definition, power rule, and a tangent-line diagram with a worked example.

316

Partial Derivatives

Differentiating multivariable functions one variable at a time, with a worked example.

305

Gradient

The vector of partial derivatives that points toward steepest increase, with a contour-plot diagram.

306

Gradient Descent

The core training algorithm behind most ML models, with a step-by-step numerical trace and learning rate comparison.

317

Chain Rule

The formula, a worked example, and why it powers backpropagation.

307

Probability for Machine Learning

Core probability definitions and formulas, and why ML reasons in probabilities rather than certainties.

318

Random Variables

Discrete vs continuous random variables, notation, and a coin-flip example.

319

Probability Distributions

Bernoulli, Binomial and Normal distributions, with formulas and a bell curve diagram.

320

Conditional Probability

The formula, a Venn diagram, and a worked spam-email example.

321

Expectation

The expected value formula, linearity of expectation, and a dice-roll example.

Data Preprocessing

16 of 16 topics published
401

Data Preprocessing

The standard preprocessing sequence — cleaning, encoding, scaling — and why order matters.

402

Data Cleaning

Fixing dtype, text and structural issues before deeper preprocessing.

403

Missing Values

MCAR, MAR and MNAR — why the type of missingness determines whether imputation is safe.

404

Missing Value Imputation

Mean, median, mode and KNN imputation compared, with a worked skewed-data example.

405

Duplicate Data

Detecting and removing exact and near-duplicate rows correctly.

406

Outlier Treatment

IQR and Z-score outlier detection formulas, a boxplot diagram, and how to treat outliers.

407

Categorical Data

Nominal vs ordinal categories, and why cardinality decides your encoding strategy.

408

Label Encoding

How LabelEncoder works, and why using it on nominal features implies a false order.

409

One-Hot Encoding

How one-hot encoding works, the dummy variable trap, and handling unseen categories in production.

410

Ordinal Encoding

Encoding genuinely ordered categories while preserving their real-world rank.

411

Feature Scaling

Why scale matters for distance- and gradient-based models, with a before/after diagram.

412

Standardization

The Z-score formula, a worked example, and why it's the default scaling choice.

413

Normalization

The Min-Max formula, a worked example, and normalization vs standardization.

414

Robust Scaling

Median/IQR-based scaling that resists outliers, with a worked numerical example.

415

Data Leakage

Preprocessing, target and temporal leakage — how each happens and how to prevent it.

416

Preprocessing Pipeline

Chaining imputation, encoding and scaling into a single reproducible scikit-learn pipeline.

Feature Engineering

15 of 18 topics published
601

Feature Engineering

Creating, transforming and selecting features — and why it often matters more than algorithm choice.

611

Feature Selection

The filter, wrapper and embedded families of feature selection compared.

608

Feature Extraction

Deriving new, compact features from raw or complex data — PCA, aggregation and text vectors.

609

Feature Transformation

Log, square root and Box-Cox transforms for fixing skewed numeric features.

602

Numerical Features

Binning, ratios and other numeric feature engineering techniques beyond basic scaling.

603

Categorical Features

Frequency encoding, target encoding, and handling rare/high-cardinality categories.

604

Date-Time Features

Extracting calendar features and cyclical sine/cosine encoding for time-based data.

605

Text Features

Bag-of-Words, the TF-IDF formula, and simple statistical text features.

606

Polynomial Features

How polynomial expansion lets linear models fit curves, with a full worked example.

607

Interaction Features

Capturing combined feature effects a linear model can't discover on its own.

610

Feature Importance

Three ways to measure feature importance, and why they can disagree.

615

Feature Engineering Best Practices

A practical checklist and before/after example for disciplined feature engineering.

612

Filter Methods

Variance threshold and correlation-based feature selection, with formulas and code.

613

Wrapper Methods

Recursive Feature Elimination (RFE) explained step by step, with scikit-learn code.

614

Embedded Methods

Lasso regularization and tree-based importance as automatic feature selection.

Model Evaluation

19 of 19 topics published
1701

Model Evaluation

The full evaluation workflow, and why classification and regression need different metrics.

1702

Train-Test Split (Concept)

Why one split isn't always reliable, and the three-way train/validation/test setup.

1703

Cross-Validation

Averaging performance across multiple splits, with the mean and std formulas.

1704

K-Fold Cross-Validation

The rotating-fold algorithm, with a diagram and full Python implementation.

1705

Stratified K-Fold

Preserving class proportions per fold, essential for imbalanced classification.

1706

Confusion Matrix

TP/TN/FP/FN defined, with a full worked example and diagram.

1707

Accuracy

The formula, a worked example, and why it's dangerously misleading on imbalanced data.

1708

Precision

The formula, a worked example, and when false positives are the costly error.

1709

Recall

The formula, a worked example, and the trap of trivially maximizing it.

1710

F1-Score

The harmonic mean formula, a worked example, and why it beats a plain average.

1711

ROC-AUC

TPR/FPR, the ROC curve diagram, and a worked threshold-by-threshold example.

1712

Precision-Recall Curve

Why it beats ROC-AUC on imbalanced data, with threshold-selection code.

1713

Log Loss

Evaluating probability calibration, not just correctness, with a worked comparison.

1714

Mean Squared Error

The MSE formula, a worked example, and why squaring creates a units problem.

1715

Mean Absolute Error

The MAE formula, a worked example, and a direct outlier-sensitivity comparison to MSE.

1716

RMSE

The square-root-of-MSE formula, a worked example, and why it's the most-reported metric.

1717

R² Score

The variance-explained formula, a worked example, and why R² can go negative.

1718

Classification Metrics

A decision table for choosing between accuracy, precision, recall, F1 and ROC-AUC.

1719

Regression Metrics

A decision table for choosing between MSE, MAE, RMSE and R².

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Machine Learning Notes – FAQs

What students search before reading Machine Learning notes.

Yes — all 247 Machine Learning topics on CodingNow 2.0 are completely free with no signup or paywall. Read them in the browser on mobile or desktop.
This hub covers 247 structured Machine Learning topics — from absolute basics to advanced, interview-ready concepts — each with short explanations and working code examples.
The notes are written to be self-study friendly, but for job-ready skills, projects and placement support, CodingNow 2.0's mentor-led Machine Learning course in Delhi (online + classroom) is the fastest path.
Yes. Each topic is concise and example-driven — ideal for last-minute revision before college exams, campus placements and Machine Learning job interviews in India.
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