CSCI417 Machine Intelligence Lecture 8

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Questions and Answers

What is the primary goal of cluster analysis?

To predict a target variable

To identify patterns in the data

To evaluate the model's performance

To group similar data points in a dataset (correct)

What type of machine learning technique is clustering?

Supervised learning

Semi-supervised learning

Unsupervised learning (correct)

Reinforcement learning

What is the outcome of running a clustering technique on a dataset?

The dataset is transformed into a different format

A new target variable is predicted

The dataset is reduced in size

A new column is added to the dataset indicating the group each row belongs to (correct)

What is the condition for effective clustering?

Low intra-cluster distance and high inter-cluster distance Signup and view all the answers

What is the purpose of clustering in real-world scenarios?

To analyze data without a target variable Signup and view all the answers

What is the role of metrics in clustering?

To evaluate the similarity between data points Signup and view all the answers

What is the characteristic of the data in cluster analysis?

Heterogeneous Signup and view all the answers

What is the type of learning that clustering belongs to?

Unsupervised learning Signup and view all the answers

What is the main difference between hard clustering and soft clustering?

In hard clustering, each data point is assigned to a single cluster, while in soft clustering, a probability is assigned to each data point belonging to a cluster Signup and view all the answers

What is the main purpose of clustering?

To group similar data points together Signup and view all the answers

What is the term for the calculation of the probability of a data point belonging to a cluster?

Likelihood evaluation Signup and view all the answers

What is the main characteristic of hierarchical clustering?

It is a set of nested clusters organized as a tree Signup and view all the answers

What is the term for the process of dividing data objects into non-overlapping subsets?

Partitional clustering Signup and view all the answers

What is the term for the distance between clusters?

Inter-cluster distance Signup and view all the answers

What is the term for the distance within a cluster?

Intra-cluster distance Signup and view all the answers

What is the main advantage of soft clustering over hard clustering?

Soft clustering provides a probability assignment for each data point Signup and view all the answers

What is the primary goal of the K-Means clustering algorithm?

To assign each data point to the closest cluster Signup and view all the answers

What is the role of a centroid in K-Means clustering?

To serve as the central point of a cluster Signup and view all the answers

How does the K-Means algorithm initialize the centroids?

By randomly selecting k data points Signup and view all the answers

What is the criterion used to assign data points to clusters in K-Means?

Euclidean distance Signup and view all the answers

What is the purpose of the iterative steps in the K-Means algorithm?

To assign data points to clusters and update centroids Signup and view all the answers

What is the main advantage of using K-Means clustering?

It is a simple and efficient algorithm for clustering Signup and view all the answers

What is the dataset used in the example to illustrate the K-Means algorithm?

Iris flower dataset Signup and view all the answers

What is the visualization used to demonstrate the clustering results in the example?

Scatter plot of petal lengths and widths Signup and view all the answers

What is the primary purpose of the first iteration in the K-Means algorithm?

To create two randomly generated centroids and assign each data point to the closest cluster Signup and view all the answers

What happens to the centroids in the second iteration of the algorithm?

They are replaced by the average values of each of the two clusters Signup and view all the answers

What is the goal of the process of choosing k in the K-Means algorithm?

To find the point at which increasing k will cause a very small decrease in the error sum Signup and view all the answers

What is the term used to describe the point where increasing k will cause a very small decrease in the error sum?

Elbow point Signup and view all the answers

Why is it not recommended to choose a k value equal to the number of data points?

Because it will result in a sum of zero Signup and view all the answers

What is an advantage of the K-Means algorithm mentioned in the text?

It is suitable for clustering large datasets Signup and view all the answers

What is the relationship between the value of k and the sum of distances between each point and its closest centroid?

As k increases, the sum always decreases Signup and view all the answers

What is the primary purpose of the K-Means algorithm?

To cluster data into groups based on similarity Signup and view all the answers

What is the key characteristic of prototype-based clusters?

They rely on representative points within each cluster Signup and view all the answers

What is the main advantage of prototype-based clustering algorithms?

They are scalable and have high interpretability Signup and view all the answers

What is the definition of a cluster in graph-based clustering?

A group of objects that are connected to one another Signup and view all the answers

When is density-based clustering typically employed?

When the clusters are irregular and when noise and outliers are present Signup and view all the answers

What is the main difference between prototype-based and graph-based clustering?

The way clusters are defined Signup and view all the answers

Which type of clustering encompasses all the previous definitions of a cluster?

Shared-property clustering Signup and view all the answers

Study Notes

Machine Intelligence: Unsupervised Machine Learning

Machine learning is a technique used in data science to group similar rows in a dataset.
After running a clustering technique, a new column appears in the dataset to indicate the group each row of data fits into best.

Cluster Analysis

In real-world scenarios, not every dataset has a target variable, making supervised learning algorithms unusable.
Unsupervised learning algorithms, such as cluster analysis, are used to analyze such data.
Cluster analysis is used to group similar data points in a dataset.

Clustering

Clustering aims to form groups of homogeneous data points from a heterogeneous dataset.
The goal is to organize data into clusters such that there is low intra-cluster distance (high similarity) and high inter-cluster distance (low similarity).
Clustering evaluates similarity based on metrics like Euclidean distance, Cosine similarity, and Manhattan distance, and groups points with the highest similarity score together.

Types of Clustering

There are two broad types of clustering: Hard Clustering and Soft Clustering.
Hard Clustering: each data point belongs to a cluster completely or not.
Soft Clustering: assigns a probability or likelihood of a data point being in a cluster.

Types of Clustering Algorithms

Hierarchical vs. Partitional Clustering: Hierarchical clustering is a set of nested clusters organized as a tree, while Partitional clustering divides data into non-overlapping subsets.
Exclusive vs. Overlapping vs. Fuzzy Clustering: Exclusive clustering assigns each data point to one cluster, Overlapping clustering allows data points to belong to multiple clusters, and Fuzzy clustering assigns a probability of a data point being in a cluster.
Complete vs. Partial Clustering: Complete clustering requires all data points to be clustered, while Partial clustering allows for some data points to remain unclustered.

K-Means Clustering

K-Means clustering is an unsupervised learning algorithm that finds a fixed number (k) of clusters in a dataset.
A cluster is defined by a centroid, which is the center point of a cluster.
K-Means finds k centroids and assigns all data points to the closest cluster.

K-Means Algorithm

The algorithm starts by randomly defining k centroids.
It iteratively assigns each data point to the closest centroid, calculates the mean of the values of all points belonging to a centroid, and updates the centroid value.
The process repeats until convergence is reached or a predetermined maximum number of iterations is reached.

Choosing K

The goal is to find the best k value by measuring the quality of the clusters.
The traditional method is to start with a random k, create centroids, and run the algorithm.
The sum of the distances between each point and its closest centroid is calculated.
The goal is to find the "elbow point" where increasing k will cause a very small decrease in the error sum, while decreasing k will sharply increase the error sum.

Prototype-based Clusters

Prototype-based clusters rely on representative points (prototypes) within each cluster.
Prototypes can be centroids (mean points) or medoids (actual data points).
K-means and K-medoids are examples of prototype-based clustering algorithms.
Advantages: simplicity, scalability, and interpretability.

Graph-based Clusters

Graph-based clusters are defined as connected components in a graph, where nodes are objects and links represent connections among objects.
An important example is contiguity-based clusters, where two objects are connected only if they are within a specified distance of each other.

Density-based Clusters

Density-based clusters are dense regions of objects surrounded by regions of low density.
This type is employed when the clusters are irregular and when noise and outliers are present.

Shared-property (Conceptual) Clusters

A cluster is a set of objects that share some property.
This definition encompasses all previous definitions of clusters.

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Description

This quiz covers topics in Machine Intelligence, including Machine Learning Basics, k-Nearest Neighbors, decision trees, and more. Test your understanding of these concepts in this lecture.