Lecture-22 Lists 24-25

COMP101 Introduction to Programming 2024-25: Lecture-22 Data Collections - Lists

Page 1: Overview

  • Introduction to data collections in programming.

Page 2: Data Assignments

  • Typically, one variable holds one data item:

    • Example: name = 'stephen'

  • Can assign several related data items to one variable:

    • Example: siblings = ['stephen', 'leszek', 'penny', 'victor', 'jenny']

    • Relationship: siblings or students in a module.

Page 3: Types of Data Collections

  • Four main data types for storing multiple values:

    • List

    • Tuple

    • Set

    • Dictionary

  • Often called 'one-dimensional arrays' (1-D arrays).

  • They are data types similar to int, float, etc., used to store multiple related data items using a single variable name.

Page 4: Lists

  • Example: siblingList = ['stephen', 'leszek', 'penny', 'victor', 'jenny']

  • Characteristics:

    • Uses brackets [ ].

    • Ordered (indexed starting at 0).

    • Mutable (can change elements).

    • Duplicates allowed.

    • Mixed data types permitted.

    • Suitable for frequent additions, amendments, or deletions, but slower access for iteration.

Page 5: Tuples

  • Example: siblingTuple = ('stephen', 'leszek', 'penny', 'victor', 'jenny')

  • Characteristics:

    • Uses parentheses ( ).

    • Ordered (indexed starting at 0).

    • Immutable (cannot change elements).

    • Duplicates allowed.

    • Mixed data types permitted.

    • Best for fixed sets of data, faster processing compared to lists for large datasets.

Page 6: Sets

  • Example: siblingSet = {'stephen', 'leszek', 'penny', 'victor', 'jenny'}

  • Characteristics:

    • Uses curly braces { }.

    • Unordered (no indexing).

    • Immutable elements.

    • No duplicates allowed.

    • Mixed data types permitted.

    • Efficient for checking membership of items.

Page 7: Dictionaries

  • Example: siblingDict = {'stephen': 'male', 'leszek': 'male', 'penny': 'female', 'victor': 'male', 'jenny': 'female'}

  • Characteristics:

    • From Python v3.7 and above.

    • Called an 'associative array' (key: value pairs).

    • Ordered (has an index).

    • Mutable with no duplicates.

    • Fast processing for large volumes of data.

    • Data retrieval via its key.

Page 8: List Indexing and Access

  • Each list element has an index, starting at [0]:

    • Example: siblingList = ['stephen', 'leszek', 'penny', 'victor', 'jenny']

    • Accessing: print(siblingList[2]) gives penny.

    • Individual characters can't be accessed; only entire elements.

Page 9: Modifying Lists

  • Example: Changing an element in a list:

    • To change penny to benny:

      siblingList[2] = 'benny'

    • Result: siblingList becomes ['stephen', 'leszek', 'benny', 'victor', 'jenny'].

Page 10: List to String Conversion

  • Use ' '.join(list) to convert list to a string:

    • E.g., siblingString = ' '.join(siblingList), results in stephen leszek benny victor jenny.

    • Method separates each element by a space (or specified separator).

Page 11: String Representation

  • Example of converting list to string:

    siblingString = ', '.join(siblingList)

    • Converts to stephen, leszek, benny, victor, jenny, indexes assigned to each character from 0 to 32.

Page 12: String to List Conversion - .split()

  • To convert string back to a list use .split(separator):

    • Example: var = string_name.split(' ') retrieves access to change individual elements.

Page 13: Further String Splitting Example

  • Example:

    siblingString = ' '.join(siblingList)
splitList = siblingString.split()

    • Converts back to the original list with indexes.

Page 14: List Slicing and Output

  • Example of slicing a list:

    print(siblingList[1:3])  # Output: ['leszek', 'benny']

  • The last index is excluded in slice notation.

Page 15: Extended Slicing Example

  • Accessing slices:

    print(siblingList[:3])  # Output: ['stephen', 'leszek', 'benny']
print(siblingList[3:])  # Output: ['victor', 'jenny']

Page 16: Slicing with Stride

  • Using stride in slicing:

    print(siblingList[::2])  # Output: ['stephen', 'benny', 'jenny']

Page 17: Extending Lists

  • Example of short names for each sibling:

    • ste for stephen, les for leszek, etc.

Page 18: Creating a New List with Short Names

  • Steps to create a list of short names:

    1. Create a new list.

    2. For each name, slice the first 3 characters.

    3. Append to the new list.

Page 19: Looping through List to Slice Names

  • Example:

    familiarList = []
for i in siblingList:
    familiarList.append(i[:3])
print(familiarList)  # Output: ['ste', 'les', 'ben', 'vic', 'jen']

Page 20: Concatenating Two Lists

  • Create a third list to combine full names and short names:

    siblingFamiliar = []
for i in range(len(siblingList)):
    siblingName = siblingList[i] + ' ' + familiarList[i]
    siblingFamiliar.append(siblingName)
print(siblingFamiliar)  # Output: ['stephen ste', 'leszek les', ...]

Page 21: Concatenation Explained

  • The concatenation combines full names with their short forms:

    • Using a + operator allows for combined elements.

Page 22: Basic List Concatenation

  • Example of concatenating different lists:

    listNum = [1, 2, 3]
listStr = ['a', 'b', 'c']
combined = listNum + listStr
print(combined)  # Output: [1, 2, 3, 'a', 'b', 'c']

Page 23: Creating and Populating Lists

  • Example of creating and populating an empty list:

    spectrumList = ['red', 'orange', 'green', 'blue']

  • Items can be any type and mixed types are allowed.

Page 24: List Output

  • Output full list and one item:

    print(spectrumList)  # Output: ['red', 'orange', 'green', 'blue']
print(spectrumList[2])  # Output: green

Page 25: Slicing for Output

  • Example of slicing for several items:

    print(spectrumList[1:3])  # Output: ['orange', 'green']

Page 26: Adding Items by Index

  • Adding items at specific indices:

    spectrumList[2:2] = ['yellow']
print(spectrumList)  # Output: ['red', 'orange', 'yellow', 'green', 'blue']

Page 27: Inserting Items

  • Example of inserting an item anywhere in a list:

    spectrumList.insert(0, 'colours')
print(spectrumList)  # Output includes 'colours' at start.

Page 28: Appending Items

  • Using .append() to add to the end of the list:

    spectrumList.append('indigo')
print(spectrumList)  # Output with 'indigo' last.

Page 29: Deleting Items by Index

  • Using del to delete items:

    del spectrumList[1]  # Removes 'orange'

Page 30: Removing by Value

  • Example of using .remove():

    spectrumList.remove('blue')
print(spectrumList)  # Removes the first 'blue' occurrence.

Page 31: List Functions

  • Count items with len():

    print(len(spectrumList))  # Output the length of spectrum list.

  • Sum numeric items using sum():

    numList = [1, 2, 3]
print(sum(numList))  # Output the total sum.

Page 32: Lists Summary

  • Example of user-defined lists:

    num_list = [1, 2, 3, 4]
animal_list = ['cat', 'dog', 'cow', 'big bird']

  • Lists are ordered and indexed.

Page 33: Accessing List Items

  • Reference to an item is via its index:

    • List indexing behavior explained:

      • First index is always [0].

      • Example shown for animalList access.