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ELEC0021 – Programming
ASSIGNMENT 2
This assignment is worth 20% of the Programming 2 mark. You must work individually
implementing 3 different algorithms (sorting, basic image processing and basic data
processing). Remember that you can discuss ideas with your classmates, but you must not
share your code with others.
The deadline for this lab submission is Monday 21st March 2022, 9am. Oral examinations
of your submitted code will take place on the last week of the term (from 21st to 25th March).
PART A: Hybrid Sort (30 points, sorting algorithms)
Hybrid Sort is an algorithm that mixes the operation principles behind Bubble Sort and
Selection Sort.
At the end of the first iteration of Bubble Sort (when sorting from smallest to largest), the
greatest value is stored in the last position of the array whilst at the end of the first iteration
of Selection Sort (when sorting from smallest to largest) the smallest element is stored in the
first position of the array.
Hybrid sort will mix both sorting algorithms in such a way that at the end of the first
iteration of the outer loop the smallest element will be found in the first position of the array
(due to Bubble Sort) and the largest element will be stored in the last position of the array
(due to Selection Sort). In the second iteration (of the outer loop), the second smallest
element will be stored in the second position of the array and (due to Bubble Sort) and the
second largest element will be stored in the penultimate position of the array, and so on.
To achieve the behaviour described above, Hybrid Sorts uses the code of Bubble Sort as the
main code and includes a part of Selection Sort in it as follows: whilst Bubble Sort compares
pairs of values in the array to decide whether to swap them or not (inner loop), Hybrid Sort
will use this very same loop to search for the minimum value in the array and store it in the
right position at the end of this inner iteration. Once the minimum value is found, it is
swapped with the number stored in the position where the minimum value should be stored
(that is the Selection Sort part).
The following table shows how the content of an array made of 5 elements ([67, 12, 44, 24,
66]) changes after each iteration of the outer loop (while loop) of Hybrid Sort:
• End of first iteration (while loop): [12, 44, 24, 66,67]
Number 67 has been bubbled up, 12 has been selected as the minimum value and
stored in first position
• End of second iteration (while loop): [12, 24, 44, 66, 67]
Number 66 has been bubbled up, 24 has been selected as the next minimum value and
stored in second position
• End of third iteration (while loop): [12, 24, 44, 66, 67]
No swap has been made, 44 is in its final position. Array is sorted
Your task: Implement the method hybridSort in the class below:
import numpy as np
class processArray:
def __init__(self,size):
self.size=2
self.setSize(size)
self.numbers=np.random.random([self.size])*100
self.numbers=self.numbers.round(0)
def __str__(self):
return “Array of “+str(self.size)+” numbers”+”\n”+str(self.numbers)
def setSize(self,size):
if(size>=2):
self.size=size
def hybridSort(self):
#your code goes here
You must submit the file processArray.py above, including your implementation of
hybridSort. You must not modify the code given here, except by adding your won code in the
method hybridSort.
Suggestion: You might want to use incremental developing to solve this problem in steps:
• Step 1: Code Bubble Sort and make sure you understand how it works. Changing
Bubble Sort to sort numbers from largest to smallest (i.e. largest element in position
0 and smallest element in the last position of the array) might help you understand
the code better.
• Step 2: Code Selection Sort and make sure you understand how it works. Changing
Selection Sort to sort numbers from largest to smallest might help you understand.
• Step 3: Modify the code of Bubble Sort (inner loop) to find the minimum value in the
unsorted part of the array in each iteration. Print this value, to make sure your code is
working correctly.
• Step 4: Further modify Bubble Sort to apply the working principle of Selection Sort.
That is, swap the minimum value found in Step 3 with the value that is occupying their
final position. Notice that in the first iteration the minimum must go into position 0,
in the second it needs to go in position 1 and so on.
• Step 5: Test your code with normal, extreme (e.g. reversed sorted data) and random
cases.
PART B: Image Filter (40 points, Numpy and Matplotlib)
Grayscale images can be stored as 2D arrays. Every element in the array is a pixel with a value
between 0 (black) and 255 (white). The Python code below uses a 2D array to create 2
images, as follows.
• Lines 1-3: Relevant modules are imported. The module matplotlib allows to read and
write image files
• Line 5: A 2D array, called image, of 300×300 elements storing the number 0 is created.
• Line 7: The 2D array image is stored as an image in the file all_black.jpg, thanks to the
method imsave available in matplotlib. The image will look like a black square of
300×300 pixels.
• Lines 9-10: The number 255 is stored in the diagonal of the array. Thus, we are adding
a white diagonal line to the original image.
• Line 12: The black square with the white diagonal line is stored in file line.jpg
import numpy as np
import random
import matplotlib.pyplot as plt
creating a black square of 300×300 pixels
image=np.zeros([300,300])
saving black square to png file
plt.imsave(‘all_black.jpg’, image, cmap=plt.cm.gray)
drawing a white diagonal
for i in range(0,300):
image[i,i]=255
saving png file
plt.imsave(‘line.jpg’, image, cmap=plt.cm.gray)
You can execute this code and open the generated files to check their content.
Image filters are nothing more than operations performed in the data of the array storing the
image. For example, the following code acts as a filter that mixes 3 images:
import numpy as np
import random
import matplotlib.pyplot as plt
creating a black square with a white diagonal
image1=np.zeros([300,300])
for i in range(0,300):
image1[i,i]=255
plt.imsave(‘diag.png’, image1, cmap=plt.cm.gray)
creating a black square with a smaller square in it
image2=np.zeros([300,300])
for i in range(100,200):
for j in range(100,200):
image2[i,j]=255
plt.imsave(‘square.png’, image2, cmap=plt.cm.gray)
creating a black square with a “reverse” white diagonal
image3=np.zeros([300,300])
for i in range(0,300):
image3[i,299-i]=255
plt.imsave(‘rev_diag.png’, image3, cmap=plt.cm.gray)
extracting 1/3 of each image and adding it in image 4
image4=np.zeros([300,300])
for j in range(0,100):
image4[:,j]=image1[:,j]
for j in range(100,200):
image4[:,j]=image2[:,j]
for j in range(200,300):
image4[:,j]=image3[:,j]
plt.imsave(‘merge.png’, image4, cmap=plt.cm.gray)
You can execute the code above and open the generated files to check their content.
Your task: Implement the methods removeNoise() and filter1() in the class noisyPattern
shown below:
import numpy as np
import random
import matplotlib.pyplot as plt
class noisyPattern:
def __init__(self):
self.image=np.full([80,80],255)
self.setLines()
def setLines(self):
self.image[:,0:16]=0
self.image[:,32:48]=0
self.image[:,64:80]=0
plt.imsave(‘lines.png’, self.image, cmap=plt.cm.gray)
def addNoise(self):
noise=0.05
for i in range (0,self.image.shape[0]):
for j in range(0,self.image.shape[1]):
if(noise > random.random()):
self.image[i,j]=255
plt.imsave(‘noisy_pattern.png’, self.image, cmap=plt.cm.gray)
def removeNoise(self):
#your code here
#if there is a white dot, replace its value by the value
# of the majority of neighbouring pixels
#save the resulting image in file noise_removed.png
def filter1(self):
#your code here
#replace the value of every pixel by the average of the values
#of its neighbouring pixels
#save the resulting image in file pattern_filter1.png
Below, you can see the contents of the files (you will need to zoom in to be able to see the
details):
• lines.png (Figure B1.a), created by the method setLines()
• noisy_pattern.png(Figure B1.b), created by the method addNoise() for noise=0.05
• noise_removed.png (Figure B1.c), the appearance of the noisy pattern after being
processed to reduce noise by the method removeNoise()
• pattern_filter1.png (Figure B.1d), the appearance of the original image (lines.png)
after applying the method filter1(). You can see how edges have been blurred.
a) lines.png b)noisy_pattern.png c)noise_removed.png d)pattern_filter1.png
Figure B1. Images used/generated by the code
The implementation of the methods removeNoise() and filter1() must follow the description
below:
• removeNoise: every white pixel (pixel containing value 255) that is surrounded by a
majority of black pixels is replaced by 0. For example, in Figure B.2, the majority of the
pixels surrounding the pixel being analysed (cell highlighted in light blue) are black
pixels. Hence, the pixel in changed to black.
0 0 255 0 0 255
0 255 0 → 0 0 0
0 0 255 0 0 255
Figure B.2. Example of noise removal in a black and white noisy image.
If the majority of pixels surrounding a white pixel is also white, no change is needed.
To keep the code easy to read, you might need to create an auxiliary private method
to determine whether the majority of neighbouring pixels are white or black. You do
not need to filter the noise in the borders of the image.
• Filter1(): the content every white pixel is replaced by the average of the values of the
pixels surrounding it. In the example shown in Figure 2, the pixel under analysis (cell
highlighted in light blue) is replaced by (255+255+255+255+255+0+0+0)/8.
0 255 255 0 255 255
0 255 255 → 0 159 255
0 255 255 0 255 255
Figure B.3. Example of filter applied to an image
To keep the code easy to read, you should create an auxiliary private method to
determine the average of the values of neighbouring pixels. You do not need to filter
the pixels in the border of the image (i.e. rows/columns 0 and 79).
Please, notice that you must not modify the code given to you, except for the methods
you need to build.
PART C: Getting started with Data Science (30 points, Strings and Pandas)
Many times, people who need to analyse the data from a csv file are not programmers. For
them, a programme that allows them to perform data processing with an easy interface is of
paramount importance.
Your task: implement the functions filtering() and plotting() for the data available in the file
athlete_events.csv available at https://www.kaggle.com/heesoo…
The description of the functions is as follows:
• filtering: this function takes a dataframe as input argument. Next, it asks the users what
features of the dataset will be used as filters, as shown in Figure C.1. Due to the limited
time you have for the assignment, this function will only filter the features Sex, Age,
Team, Year and Sport.
Figure C.1. Initial information presented to the user
The user can then enter their choices. For example, if the user enters number 3, it means
that they want to filter using the Team feature only. Instead, if the user enters 145, it
means the user wants to filter the data based on the features of Sex, Year and Sport. If
the user enters 12345, it means they want to filter the data based on the 5 features.
If the user enters an invalid number (i.e. more than 5 digits or any individual digit
higher than 5), the execution stops and a message is displayed, as shown in Figures C.2
and C.3.
Figure C.2. Programme behaviour when the user enters more than 5 digits
Figure C.3. Example of the programme behaviour when user enters a nonvalid
number
If the user enters a valid option, the system asks about the value of the features, as
shown in Figure C.4. In this case, the user has entered the number 125, meaning they
want to filter using the features of Sex, Age and Sport. Thus, the programme asks for the
values the user wants to use for each of those features.
Figure C.4. Requesting additional information to the user
Next, the function must filter the data and store the filtered data in a new dataframe
made only of the rows with the athletes data that match the request made by the user.
In the example of Figure C.4. that means filtering the rows that comply with Sex being
equal to F, Age being equal to 21 and Sport being equal to Judo.
Finally, the function filtering returns the number of records of the new dataframe
and the new dataframe itself (the one with the filtered data). In the cases of error
(exemplified in Figures C.2 and C.3) the function must return zero (zero numbers of
records) and the original dataframe.
• plotting: this function takes two input arguments: the number of records of a
dataframe and the dataframe. First, it prints the number of records received. Next, if
the number of rows of the dataframe is lower than 100 (and higher than 0), it
generates a scatter plot of the weight of the athletes (horizontal axis is the ID of the
athletes). This plot must be saved in a file called scatter.png and the message“File
scatter.png saved”must be printed on screen. If the number of records is higher than
or equal to 100, the function generates a histogram of the weight using 12 bins. This
plot must be saved in a file called hist.png and the message“File hist.png saved”must
be printed on screen. If the number of rows is equal to 0, no plot is generated. Please,
see an example of the information printed on screen in Figure C.5.
Figure C.5. Example of information printed on screen by the programme under
normal operation
