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🔍 Machine Learning Cheat Sheet 🔍

1. Key Concepts:
- Supervised Learning: Learn from labeled data (e.g., classification, regression).
- Unsupervised Learning: Discover patterns in unlabeled data (e.g., clustering, dimensionality reduction).
- Reinforcement Learning: Learn by interacting with an environment to maximize reward.

2. Common Algorithms:
- Linear Regression: Predict continuous values.
- Logistic Regression: Binary classification.
- Decision Trees: Simple, interpretable model for classification and regression.
- Random Forests: Ensemble method for improved accuracy.
- Support Vector Machines: Effective for high-dimensional spaces.
- K-Nearest Neighbors: Instance-based learning for classification/regression.
- K-Means: Clustering algorithm.
- Principal Component Analysis(PCA)

3. Performance Metrics:
- Classification: Accuracy, Precision, Recall, F1-Score, ROC-AUC.
- Regression: Mean Absolute Error (MAE), Mean Squared Error (MSE), R^2 Score.

4. Data Preprocessing:
- Normalization: Scale features to a standard range.
- Standardization: Transform features to have zero mean and unit variance.
- Imputation: Handle missing data.
- Encoding: Convert categorical data into numerical format.

5. Model Evaluation:
- Cross-Validation: Ensure model generalization.
- Train-Test Split: Divide data to evaluate model performance.

6. Libraries:
- Python: Scikit-Learn, TensorFlow, Keras, PyTorch, Pandas, Numpy, Matplotlib.
- R: caret, randomForest, e1071, ggplot2.

7. Tips for Success:
- Feature Engineering: Enhance data quality and relevance.
- Hyperparameter Tuning: Optimize model parameters (Grid Search, Random Search).
- Model Interpretability: Use tools like SHAP and LIME.
- Continuous Learning: Stay updated with the latest research and trends.

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Snowflake schema in Power BI:

1. What is a Snowflake Schema and how does it differ from other schema types like Star schema?

Snowflake Schema: A data modeling technique where a single fact table is connected to multiple dimension tables, and these dimension tables are further normalized into sub-dimension tables.
Star Schema: All dimension tables directly connect to the fact table.

2. What are the Advantages and Disadvantages of using a Snowflake Schema in Power BI?

Advantages:
-Improved data integrity and normalization.
-Flexibility in managing and updating dimension tables independently.
Disadvantages:
-Complex relationships can lead to longer query execution times.
-May require more joins and relationships to retrieve data.
-Potential performance issues with large or complex datasets.

3. How do you Implement a Snowflake Schema in Power BI Data Modeling?

- Create a fact table and multiple dimension tables.
-Split dimension tables into sub-dimension tables based on attributes.
- Establish relationships between the fact table and dimension tables using appropriate keys.
-Use DAX functions and optimizations to handle complex joins and queries efficiently.

4. How do you Handle Hierarchies and Drill-Through in a Snowflake Schema in Power BI?

-Create hierarchies within dimension tables to organize and navigate data levels.
- Implement drill-through actions to navigate from summary to detailed data views by clicking on data points in visuals.

5. What are Best Practices for Implementing a Snowflake Schema in Power BI?
-Plan and design tables, keys, and relationships carefully.
-Normalize dimension tables to reduce redundancy and improve data integrity.
- Optimize queries, indexes, and relationships for better performance.
-Document schema design, relationships, calculations, and assumptions for clarity and maintenance.
-Validate and test the Snowflake schema with sample data and real-world scenarios to ensure accuracy, efficiency, and reliability.

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