Accessing an Element


1. Positive Indexing

  • Definition: Accessing elements using their position from the start of the list.
  • Indexing Starts: From 0.
  • Example:
    • For a list: my_list = [10, 20, 30, 40, 50]
    • Accessing elements:
      • my_list[0] → 10 (first element)
      • my_list[1] → 20 (second element)
      • my_list[2] → 30 (third element)

2. Negative Indexing

  • Definition: Accessing elements using their position from the end of the list.
  • Indexing Starts: From -1 for the last element.
  • Example:
    • For the same list: my_list = [10, 20, 30, 40, 50]
    • Accessing elements:
      • my_list[-1] → 50 (last element)
      • my_list[-2] → 40 (second to last element)
      • my_list[-3] → 30 (third to last element)

Summary

  • Use positive indexing (0, 1, 2, ...) to access elements from the start.
  • Use negative indexing (-1, -2, -3, ...) to access elements from the end.

This allows you to easily access any element in a list!

(Javascript):

%%js
let aList = [];
while (true) {
    let user_input = prompt("Enter an item you want (or 'q' to quit):");
    if (user_input.toLowerCase() === 'q') {
        break;
    }
    aList.push(user_input);
}
// Access and display the second element (index 1)
console.log("The second thing on your list is: " + aList[1]);

(Python):

aList = []
while True:
    user_input = input("Enter an item you want (or 'q' to quit): ")
    if user_input.lower() == 'q':
        break
    aList.append(user_input)
//Displaying the second element (index 1)
if len(aList) > 1:
    print("The second thing on your list is", aList[1])
else:
    print("There is no second item in your list.")
//Display a range of data from index 1 to 3 (non-inclusive)
print("Here is a range of data (index 1 to 3):", aList[1:3])


Deleting an Element


  1. Using remove(value): Removes the first occurrence of a specified value from the list(Python).

  2. Using pop(index): Removes and returns the element at the given index. If no index is provided, it removes the last element(Python & Javascript).

  3. Using del: Deletes an element at a specified index or can remove the entire list(Python).

  4. Using splice(start, deleteCount) (JavaScript): Modifies the array by removing elements starting at a specified index(Javascript).

These methods allow you to effectively delete elements from lists or arrays in programming!

Examples(JavaSript):

%%js
let aList = [];
while (true) {
    let user_input = prompt("Enter an item you want (or 'q' to quit):");
    if (user_input.toLowerCase() === 'q') {
        break;
    }
    aList.push(user_input);
}
// Display the full list
console.log("This is your list: ", aList);
// Delete the second element (index 1)
aList.splice(1, 1);
// Display the list after deletion
console.log("This is your new list: ", aList);

(Python):

aList = []
while True:
    user_input = input("Enter an item you want (or 'q' to quit): ")
    if user_input.lower() == 'q':
        break
    aList.append(user_input)
print("This is your list:", aList)
# Deleting the second item (index 1)
if len(aList) > 1:
    del aList[1]
    print("This is your new list after deleting the second item:", aList)
else:
    print("There is no second item to delete.")

Explanation:

Accessing an Element:

The code first asks the user to input items into the list/array. It then checks if there are at least two elements and prints the second one (index 1). If not, it displays a message stating there is no second item.

Deleting an Element:

The code removes the second element from the list/array using del in Python and splice() in JavaScript, and then prints the updated list/array. If there is no second item, a message is displayed instead.

Popcorn Hack: Accessing and Deleting Elements

  • Create a list/array named aList.
  • Input items into the list/array. After the user is done adding items, display the second element (if it exists) in the list/array.
  • After adding items to the list/array, delete the second element (if it exists) and display the updated list/array.