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# Assignment 2 – Clustering

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CS 383 – Machine Learning
Assignment 2 – Clustering
Introduction
In this assignment you’ll work on clustering data.
You may not use any functions from machine learning library in your code, however you may use
statistical functions. For example, if available you MAY NOT use functions like
• kmeans
however you MAY use basic statistical functions like:
• std
• mean
• cov
• eig
• In addition, since the spirit of this assignment is not (necessarily) about feature reduction, you
may use functions like pca.
Although all assignments will be weighed equally in computing your homework grade, below is the
grading rubric we will use for this assignment:
Part 1 (Theory) 0pts
Part 2 (K-Means Clustering) 75pts
Part 3 (Purity) 25pts
TOTAL 100pts
1
DataSets
Pima Indians Diabetes Data Set In this dataset of 768 instances of testing Pima Indians for
diabetes each row has the following information (1 class label, 8 features).
0. Class Label (-1=negative,+1=positive)
1. Number of times pregnant
2. Plasma glucose concentration
3. Diastolic blood pressure (mm Hg)
4. Triceps skin fold thinkness (mm)
5. Insulin (mu U/ml)
6. Body mass index (kg/m2
)
7. Diabetes pedigree function
8. Age (yrs)
Data obtained from: https://archive.ics.uci.edu/ml/datasets/Pima+Indians+Diabetes
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1 Theory
None
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2 Clustering
Let’s implement our own version of k-means to cluster data!
Write a script that:
1. Reads in the data. For demonstrative purposes, you will be using the dataset mentioned in
Datasets section (i.e. the diabetes dataset). However, given another dataset’s observable data
matrix, X, your code should still work.
2. Separates the class label from the observable data to form matrices Y and X, respectively.
3. Standardizes the features.
4. Passes the observable data X to a (user-created) function called myKMeans that takes two
parameters:
(a) The data to cluster, X
(b) The number of clusters, k
The myKMeans function :
Your myKMeans function should run k-means on the supplied data and value of k. Since we’ll
visualize the clustering process, a few caveats:
• Although theoretically your code should work for any value of 1 <= k <= N, we’ll constrain
k to have a maximum value of 7, so that you will only need to define up to 7 colors.
• Although your code should be written in such a way to be able to cluster in any dimensional
space, for visualization purposes, if your data’s dimenionality is greater than 3, first reduce its
dimensionality to 3 using PCA. You may use the code you developed in HW1 to do this, or a
PCA function from your linear algebra library.
In order to visualize the cluster process, you’ll generate a video. Choose a frame rate that is
natural for observing the changes in the association. Each frame of the video will be a plot showing
the current clustering. If X has only 2 features, this will be a 2D plot. If it has 3 features (either
natively, or after PCA reduction), then this will be a 3D plot. If possible (that is, if the graphics
library you are using allows it), try to have any 3D plots rotated so that it is easier to see what’s
going on.
For each frame/plot you should:
1. Display the current reference vectors as solid circles and the observations as x’s.
2. The reference vectors and associated observations should have the same colors. For instance, if
you use blue to represent cluster 1, then its reference vector should be a solid blue circle, and
all observations associated with it should be blue x’s.
3. At the top of your graph you should state the iteration number.
Figures 1-2 show the initial and terminal clusterings when k = 2.
4
Implementation Details
1. Seed your random number generator with zero (do this right before running your k-means).
2. Randomly select k observations and use them for the initial reference vectors. I suggest you
use randomize the indices and use the first k randomized indices to select the observations.
3. Use the L2 distance (Euclidean) to measure the distance between observations and reference
vectors.
4. Terminate the training process when the sum of magnitude of change of the cluster centers (from
the previous iteration to the current one) is less than  = 2−23. That is, when Pk
i=1 d(ai(t −
1), ai(t)) <  where k is the number of clusters, ai(t) is the reference vector for cluster i at
time t and d(x, y) is the L1 distance (Manhattan) between vectors x and y (as defined in the
Similarity and Distance Functions link on BBlearn).
Figure 1: Initial Clustering
5
Figure 2: Final Clustering
6
3 Purity
Augment your code from Part 1 to include the purity of the clusterings at each iteration on the plot.
In order to compute the purity, use the class label information (-1=negative for diabetes, +1=positive
for diabetes). Add the current purity value to the text displayed on your figures.
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Submission
1. Source Code – Including any necessary makefiles, etc..
2. readme.txt file – The readme.txt file should contain information on how to run your code to
3. Sample videos of at least three different runs where you vary k and/or the features used. At
least one of these must use more than two features. If you were able to get the purity part
working, then these videos will include the purity in text within each frame. The video filenames
should be in the format
K [k] F [f].[ext]
where:
(a) [k] is the value of k passed to your function.
(b) [f] is an underscore-separated list of the features passed in to your kmeans function. If
you used all the features, just state all.
(d) [ext] is the file extension.
For example, in the example in Part 2, the file name would be
K 2 F all.avi
Do not include spaces or special characters (other than the underscore character) in your file and
directory names. Doing so may break our grading scripts.
Since there is no theory component to this assignment, and the visualization is a video, there is no
PDF for this assignment.
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