# Records, Lists & Tuples ## Records ### What is a record?

A record is a row in a file that is composed of multiple fields

- Commonly used in databases to represent individual entries - Each field within a record stores a specific piece of information **Example database table:** | studentID | firstName | surname | |-----------|-----------|---------| | 1001 | Sarah | Johnson | | 1002 | Marcus | Chen | | 1003 | Olivia | Patel | - The table above contains 3 records - Each record has 3 fields - A record can be declared as a custom data type ### Example in Pseudocode ```text studentDataType = record integer studentID string firstName string surname endRecord ``` ### Example in Python ```python class Student: def __init__(self, studentID, firstName, surname): self.studentID = studentID self.firstName = firstName self.surname = surname # Creating an instance of the Student record student_record = Student(1001, "Sarah", "Johnson") # Accessing the fields of the Student record print("ID:", student_record.studentID) print("First Name:", student_record.firstName) print("Surname:", student_record.surname) ``` - A class is defined called "Student" with an `__init__` method that initialises the fields of the record - Create an instance of the "Student" record called `student_record` with an ID of 1001, first name "Sarah", and surname "Johnson" - Access and print the values of the fields using dot notation (`object.field`) ### Example in Java ```java public class Student { private int studentID; private String firstName; private String surname; public Student(int studentID, String firstName, String surname) { this.studentID = studentID; this.firstName = firstName; this.surname = surname; } public int getStudentID() { return studentID; } public String getFirstName() { return firstName; } public String getSurname() { return surname; } public void setStudentID(int studentID) { this.studentID = studentID; } public void setFirstName(String firstName) { this.firstName = firstName; } public void setSurname(String surname) { this.surname = surname; } } ``` - Define a class called 'Student' with private fields for studentID, firstName, and surname - A constructor allows you to set these fields when creating an instance of the record - Getter and setter methods for each field provide controlled access and modification of values - To use the record in Java, create an instance of the 'Student' class and set or retrieve the field values using the provided methods **Example usage:** ```java public class Main { public static void main(String[] args) { Student studentRecord = new Student(1001, "Sarah", "Johnson"); // Accessing the fields of the Student record int studentID = studentRecord.getStudentID(); String firstName = studentRecord.getFirstName(); String surname = studentRecord.getSurname(); System.out.println("ID: " + studentID); System.out.println("First Name: " + firstName); System.out.println("Surname: " + surname); } } ``` - This creates an instance of the 'Student' record called `studentRecord` with an ID of 1001, first name "Sarah", and surname "Johnson" - The getter methods retrieve the field values and print them to the console ## Lists ### What is a list?

A list is a data structure that consists of a number of items where items can occur more than once

- Lists are similar to 1D arrays and elements can be accessed in the same way - The difference is that list values are stored **non-contiguously** - This means they do not have to be stored next to each other in memory, which is different to how data is stored for arrays - Lists can contain elements of more than one data type, unlike arrays ### Example in Pseudocode ```text list animals = ["elephant", "tiger", "penguin", "dolphin"] ``` ### Example in Python ```python animals = ["elephant", "tiger", "penguin", "dolphin"] ``` ### Example in Java ```java import java.util.ArrayList; import java.util.List; public class Main { public static void main(String[] args) { List animals = new ArrayList<>(); // Adding elements to the animals list animals.add("elephant"); animals.add("tiger"); animals.add("penguin"); animals.add("dolphin"); // Printing the elements in the animals list for (String animal : animals) { System.out.println(animal); } } } ``` ### Worked Example **Question:** A programmer has written the following code designed to take in ten student names then print them in a numbered list. ```python student1 = input("Enter a name: ") student2 = input("Enter a name: ") student3 = input("Enter a name: ") student4 = input("Enter a name: ") student5 = input("Enter a name: ") student6 = input("Enter a name: ") student7 = input("Enter a name: ") student8 = input("Enter a name: ") student9 = input("Enter a name: ") student10 = input("Enter a name: ") print("1. " + student1) print("2. " + student2) print("3. " + student3) print("4. " + student4) print("5. " + student5) print("6. " + student6) print("7. " + student7) print("8. " + student8) print("9. " + student9) print("10. " + student10) ``` It has been suggested that this code could be made more efficient and easier to maintain using an array or a list. Write a more efficient version of the programmer's code using an array or a list. **(5 marks)** --- **Answer:** Start by having a variable `students` which is initialised as an empty list `[]` ```python students = [] ``` Then have a for loop run from `i = 0` to `i = 9` (inclusive), indicating that it will iterate 10 times ```python for i in range(10): ``` Inside the loop, the `input()` function is used to prompt the user to enter a name. The entered name is then appended to the students list using the `append()` method ```python students.append(input("Enter a name: ")) ``` After the first for loop finishes executing, the list `students` will contain 10 names entered by the user Then a second for loop also runs from `i = 0` to `i = 9` (inclusive) ```python for i in range(10): ``` Inside this loop, the `print()` function is used to display the index of each name (incremented by 1) along with the name itself. The expression `i + 1` represents the current index, and `(i + 1) + "."` is concatenated with `students[i]` to form the output string ```python print(str(i+1) + ". " + students[i]) ``` The loop repeats this process for each name in the students list, printing the index number and corresponding name on separate lines **Example answer that gets full marks:** ```text students = [] for i = 0 to 9 students.append(input("Enter a name: ")) next i for i = 0 to 9 print((i+1) + ". " + students[i]) next i ``` **Mark scheme:** - Declaration of list/array **[1]** - For loop that runs ten times **[1]** - Inputting name to correct location each iteration **[1]** - For/while loop which outputs each name **[1]** - Names are formatted with numbers 1-10 and a dot preceding each one **[1]** ### Manipulating Lists There are a range of operations that can be performed involving lists: | List Operation | Description | Pseudocode | |----------------|-------------|------------| | `isEmpty()` | Checks if the list is empty | `Animals.isEmpty()` | | `append(value)` | Adds a new value to the end of the list | `Animals.append(lion)` | | `remove(value)` | Removes the value the first time it appears in the list | `Animals.remove(tiger)` | | `length()` | Returns the length of the list | `Animals.length()` | | `index(value)` | Returns the position of the item | `Animals.index(penguin)` | | `insert(position, value)` | Inserts a value at a given position | `Animals.insert(2, giraffe)` | | `pop()` | Returns and removes the last value | `Animals.pop()` | ## Tuples ### What is a Tuple?

A tuple is an ordered set of values of any type that is immutable

- It is **immutable**, this means that it can't be changed - Elements cannot be added or removed once it has been created - Tuples are initialised using regular brackets `()` instead of square brackets `[]` - Elements in a tuple are accessed in a similar way to elements in an array, with the exception that values can't be changed ### Example in Pseudocode ```text tuple1 = (10, 20, 30) ``` ### Example in Python ```python coordinates = ("London", 51.5074, -0.1278) print(coordinates) ``` ## When should Arrays, Records, Lists & Tuples be used? | Data Structure | Appropriate Usage | Possible use cases | |----------------|-------------------|-------------------| | **Array** | A fixed-size collection of elements and need random access to elements by index. They are efficient for accessing elements by index but less efficient for dynamic resizing or insertion/removal of elements in the middle. | - List of exam scores
- A table of values for a conversion chart
- A grid of pixels for a display | | **Records** | A group of related data which is a single entity. They are useful for organising and manipulating data with different attributes or fields. | - An employee record in a payroll system
- A transaction record in an online shop
- A booking record in a hotel system | | **Lists** | A dynamic collection of elements that may change in size. They provide flexibility for adding, removing and modifying elements. | - A shopping basket
- A task list
- A playlist of songs | | **Tuples** | An ordered, immutable collection of elements. Use when you need to ensure data cannot be modified after creation. | - GPS coordinates (latitude, longitude)
- RGB color values (red, green, blue)
- Date and time (year, month, day, hour, minute) |