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Questions and Answers
What is the primary goal of K-means clustering?
Which of the following best describes a characteristic of DBSCAN?
What is a primary limitation of K-means clustering?
Which evaluation metric is commonly used to assess the performance of clustering algorithms?
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What characteristic of DBSCAN makes it suitable for anomaly detection?
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Which process does Agglomerative Clustering follow?
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In hierarchical clustering, what does the term 'linkage' refer to?
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How do Gaussian Mixture Models (GMMs) identify clusters?
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What is a primary advantage of using Gaussian Mixture Models (GMM) over K-means clustering?
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What type of data is primarily utilized in unsupervised learning techniques such as clustering?
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What is a significant disadvantage of DBSCAN?
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What does the dendrogram produced by Agglomerative Clustering represent?
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When performing K-means clustering, what is the role of the centroid?
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What is a limitation of the K-means clustering algorithm?
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Which technique is employed by Gaussian Mixture Models during the clustering process?
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What is the primary advantage of increasing the number of random initializations in K-means?
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What is the primary function of K-means clustering?
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Which of the following describes the bottom-up approach in hierarchical clustering?
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Which of the following is a common performance evaluation metric for clustering algorithms?
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What differentiates Gaussian Mixture Models (GMM) from K-means clustering?
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Which characteristic is associated with the DBSCAN clustering algorithm?
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In K-means clustering, what is the process after initializing K random points as cluster centers?
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What is a potential challenge faced in unsupervised learning approaches such as clustering?
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Which of the following statements about clustering algorithms is false?
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Study Notes
Machine Learning 101
- Supervised learning uses labelled datasets for training, aiming to learn a mapping from inputs to outputs.
- Supervised learning can be categorized as regression (continuous response) or classification (categorical response).
- Unsupervised learning uses unlabeled data for training, aiming to discover patterns, clusters, or relationships within the data.
- Unsupervised learning is helpful for uncovering patterns and structures, and can serve as a preprocessing or post-processing step for supervised learning.
- Real-world applications include customer segmentation, anomaly detection, and recommendation systems.
Unsupervised Learning: Challenges
- Difficulty evaluating performance due to the lack of ground truth.
- Each algorithm has its own specific limitations.
Clustering
- Clustering aims to group similar instances together based on their features.
Clustering Algorithms
- Partition algorithms (flat): K-means, DB-Scan, Spectral Clustering, Mixture of Gaussian.
- Hierarchical algorithms: bottom-up (agglomerative), top-down (divisive).
K-means
- An iterative clustering algorithm, initializing by picking random points as cluster centers.
- Alternates between assigning data points to the closest cluster center and updating the cluster centers based on the assigned points.
- Can be sensitive to the initial cluster center placement, especially when dealing with unevenly sized clusters.
- Increasing the number of random initializations can help mitigate this sensitivity.
Limitations of K-means
- Can struggle with clusters of varying densities, non-spherical shapes, and clusters with different sizes.
- For complex datasets, consider alternative clustering algorithms.
DBSCAN
- Density-Based Spatial Clustering of Applications with Noise.
- Does not require specifying the number of clusters beforehand.
- Capable of finding clusters of arbitrary shapes and sizes.
- Robust to noise and outliers.
Hierarchical Clustering
-
Agglomerative Clustering:
- Starts by merging very similar instances.
- Incrementally builds larger clusters from smaller ones.
- Produces a dendrogram representing a family of clusterings.
-
Divisive Clustering:
- Starts with one cluster and repeatedly divides it into smaller clusters.
Agglomerative Clustering: Closest Clusters
- Different methods exist for defining "closeness" between clusters, including:
- Single Linkage: Distance between the closest two points in different clusters.
- Complete Linkage: Distance between the furthest two points in different clusters.
- Average Linkage: Average distance between all pairs of points from different clusters.
Gaussian Mixture Models
- Model data as a mixture of multiple Gaussian distributions.
- Expectation Maximization (EM) algorithm is used for fitting:
- E-step: Calculate the probability of each data point belonging to each Gaussian component.
- M-step: Update the parameters (mean, variance, weights) of each Gaussian component.
- Convergence Check: Repeat until convergence is reached.
- Can be computationally expensive but can be scaled to large datasets using efficient techniques.
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Description
Explore the fundamentals of machine learning, focusing on supervised and unsupervised learning techniques. Learn about clustering algorithms and their real-world applications, alongside the challenges in unsupervised learning. This quiz is ideal for beginners seeking to understand key concepts in machine learning.
