Day 6 of Learning Python for Data Science: Mastering Lists, Sets, and Logical Thinking

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Introduction to Data Structures

Data structures are the backbone of programming, enabling efficient organization and manipulation of data. Python provides several built-in data structures, such as:

  • Lists – Ordered collections of elements that allow duplicates.
  • Tuples – Immutable sequences for fixed data storage.
  • Sets – Unordered collections containing only unique elements.
  • Dictionaries – Mappings of key-value pairs for fast lookups.

In practical applications:

  • A list can store a class’s student names.
  • A set ensures roll numbers remain unique.
  • Ordered collection means list will store the elements in order of insertion.
  • Unordered collection means set does not maintain the order of insertion and each time you try accessing the collection the order will be different.

Lists

Definition and Properties

A list is a mutable, ordered collection that can store multiple data types.

Creating a list

students = ["Alice", "Bob", "Charlie"]
print(students)  # Output: ['Alice', 'Bob', 'Charlie']

Common List Operations

Python offers several methods for manipulating lists:

Adding elements

students.append("David")  # Appends 'David' at the end
students.insert(1, "Eve")  # Inserts 'Eve' at index 1

Removing elements

students.remove("Bob")  # Removes 'Bob'
students.pop()  # Removes the last element

Slicing lists

print(students[1:3])  # Outputs elements from index 1 to 2

Modifying elements

name = ['Vishal', 'Deepanjan', 'Satyam']
name[0] = 'Jaiswal'
print(name)
['Jaiswal', 'Deepanjan', 'Satyam']

Common List Methods:

append() – Adds an element at the end of the list.

students = ["Alice", "Bob"]
students.append("Charlie")
print(students)  # Output: ['Alice', 'Bob', 'Charlie']

insert() – Inserts an element at a specific index.

students.insert(1, "David")
print(students)  # Output: ['Alice', 'David', 'Bob', 'Charlie']

remove() – Removes a specific element from the list.

students.remove("Bob")
print(students)  # Output: ['Alice', 'David', 'Charlie']

pop() – Removes and returns the last element.

last_student = students.pop()
print(last_student)  # Output: 'Charlie'
print(students)  # Output: ['Alice', 'David']

Slicing (list[start:end]) – Extracts a portion of the list.

numbers = [10, 20, 30, 40, 50]
print(numbers[1:4])  # Output: [20, 30, 40]

len() – Returns the number of elements in the list.

print(len(numbers))  # Output: 5

sort() – Sorts the list in ascending order.

numbers.sort()
print(numbers)  # Output: [10, 20, 30, 40, 50]

reverse() – Reverses the elements of the list.

numbers.reverse()
print(numbers)  # Output: [50, 40, 30, 20, 10]

index() – Returns the index of the first occurrence of an element.

print(numbers.index(30))  # Output: 2

Sets

Definition and Significance

A set is an unordered, mutable collection that stores only unique elements.

Creating a set

unique_numbers = {1, 2, 3, 3, 4, 5}
print(unique_numbers)  # Output: {1, 2, 3, 4, 5}

Set Operations

Python supports various set operations for mathematical and logical manipulations:

Common Set Methods:

union() – Combines two sets, removing duplicates.

set1 = {1, 2, 3}
set2 = {3, 4, 5}
print(set1.union(set2))  # Output: {1, 2, 3, 4, 5}

intersection() – Returns common elements between two sets.

print(set1.intersection(set2))  # Output: {3}

difference() – Returns elements present in the first set but not in the second.

print(set1.difference(set2))  # Output: {1, 2}

len() – Returns the number of elements in a set.

print(len(set1))  # Output: 3

add() – Adds a single element to the set.

set1.add(6)
print(set1)  # Output: {1, 2, 3, 6}

update() – Adds multiple elements to the set.

set1.update([7, 8, 9])
print(set1)  # Output: {1, 2, 3, 6, 7, 8, 9}

discard() – Removes an element from the set without error if it doesn’t exist.

set1.discard(2)
print(set1)  # Output: {1, 3, 6, 7, 8, 9}

remove() – Removes an element but raises an error if it doesn’t exist.

set1.remove(3)
print(set1)  # Output: {1, 6, 7, 8, 9}

pop() – Removes and returns an arbitrary element from the set.

print(set1.pop())  # Output: (random element from the set)

clear() – Removes all elements from the set.

set1.clear()
print(set1)  # Output: set()

issubset() – Checks if all elements of a set exist in another set.

set1 = {1, 2, 3}
set2 = {1, 2, 3, 4, 5}
print(set1.issubset(set2))  # Output: True

issuperset() – Checks if a set contains all elements of another set.

print(set2.issuperset(set1))  # Output: True

isdisjoint() – Returns True if two sets have no common elements.

set3 = {6, 7, 8}
print(set1.isdisjoint(set3))  # Output: True

copy() – Returns a shallow copy of the set.

set_copy = set1.copy()
print(set_copy)  # Output: {1, 2, 3}

Practice Questions

  • Create a list of five student names and print it.
  • Add a new student name to the end of the list using the appropriate method.
  • Insert a student name at the second position in the list.
  • Remove a specific student name from the list.
  • Remove and return the last element of the list.
  • Retrieve a sublist containing elements from index 2 to 4 using slicing.
  • Find the index of a specific student name in the list.
  • Sort a list of integers in ascending order.
  • Reverse the order of elements in a list.
  • Count the number of times a specific element appears in a list.
  • Find the length of a given list.
  • Create a set containing five unique numbers and print it.
  • Add a new element to the set.
  • Try adding a duplicate element to the set and observe the output.
  • Remove an element from the set using the appropriate method.
  • Perform a union operation between two sets and print the result.
  • Find the common elements between two sets using the intersection method.
  • Find the elements that exist in the first set but not in the second set using the difference method.
  • Check if one set is a subset of another set.
  • Check if two sets have no common elements using the appropriate method.
  • Write a Python program to count the number of occurrences of each element in a given list.
  • Create a set of numbers from 1 to 10. Find all the numbers that are divisible by 3 using a set operation.
  • Given two lists of integers, write a program to find the elements that are common in both lists using a set.
  • Write a program to remove duplicate words from a given string and display the unique words in alphabetical order.
  • Create a list of mixed data types (e.g., numbers and strings). Write a program to separate the strings and numbers into two different lists.
  • Write a function that returns the second largest number from a list of integers. Example: [10, 20, 4, 45, 99] → Output: 45
  • Given a list and an integer k, shift elements to the right by k positions. Example: ([1, 2, 3, 4, 5], k=2) → Output: [4, 5, 1, 2, 3]
  • Given a list, remove duplicate elements while maintaining the order. Example: [1, 2, 2, 3, 4, 4, 5] → Output: [1, 2, 3, 4, 5]
  • Given a list and a target sum, find all unique pairs whose sum equals the target. Example: ([1, 2, 3, 4, 5, 6], target=7) → Output: [(1, 6), (2, 5), (3, 4)]
  • Implement a function that finds the index of a given element in a list manually. Example: ([10, 20, 30, 40], target=30) → Output: 2
  • Write a function that returns elements that exist in either of the two sets but not both. Example: {1, 2, 3, 4} and {3, 4, 5, 6} → Output: {1, 2, 5, 6}
  • Given two sets, determine if one set is a subset of the other. Example: {1, 2} is a subset of {1, 2, 3, 4} → Output: True
  • Given multiple sets, find the total count of unique elements across all sets. Example: [{1, 2, 3}, {3, 4, 5}, {5, 6, 7}] → Output: 7
  • Given three sets, find the elements that are common in all three. Example: {1, 2, 3}, {2, 3, 4}, {3, 4, 5} → Output: {3}
  • Remove all elements of set2 from set1 without using a loop. Example: {1, 2, 3, 4, 5} minus {3, 4} → Output: {1, 2, 5}
  • Given a list of integers, find the length of the longest consecutive elements sequence. Example: [100, 4, 200, 1, 3, 2] → Output: 4 ([1, 2, 3, 4] is the longest sequence)
  • Rearrange a sorted list so that the first element is the smallest, the second is the largest, the third is the second smallest, and so on. Example: [1, 2, 3, 4, 5, 6, 7] → Output: [1, 7, 2, 6, 3, 5, 4]
  • An element is a majority if it appears more than n/2 times in a list of size n. Find it in O(n) time. Example: [3, 3, 4, 2, 4, 4, 2, 4, 4] → Output: 4
  • Given two sets of numbers, find all pairs (a, b) where a is from set1, b is from set2, and (a + b) is even. Example: {1, 2, 3} and {4, 5, 6} → Output: {(2, 4), (2, 6), (1, 5), (3, 5)}

Click here for solutions – Python Practice Questions & Solutions

Conclusion

On Day 6 of Python Learning, we explored:

  • The characteristics and manipulation of lists.
  • The properties and advantages of sets.
  • Problem-solving strategies involving lists and sets.

Mastering these concepts will significantly enhance your data-handling skills in Python, paving the way for advanced topics in data science and algorithm design.

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