Python program to test if all y occur after x in List

When it is required to check if all 'y' occurs after 'x' in a list, the enumerate function along with a specific condition is used to compare indices.

Example

Below is a demonstration of the same ?

my_list = [11, 25, 13, 11, 64, 25, 8, 9]

print("The list is :")
print(my_list)

x, y = 13, 8

x_index = my_list.index(x)

my_result = True
for index, element in enumerate(my_list):
    if element == y and index < x_index:
        my_result = False
        break

if(my_result == True):
    print("All y elements occur after x elements")
else:
    print("All y elements don't occur after x elements")

Output

The list is :
[11, 25, 13, 11, 64, 25, 8, 9]
All y elements occur after x elements

Method Using List Comprehension

We can also solve this using list comprehension to find indices of all occurrences ?

my_list = [11, 25, 13, 11, 64, 25, 8, 9]

print("The list is :")
print(my_list)

x, y = 13, 8

# Find first occurrence of x
x_index = my_list.index(x)

# Find all indices of y
y_indices = [i for i, val in enumerate(my_list) if val == y]

# Check if all y indices are greater than x index
all_after = all(i > x_index for i in y_indices)

if all_after:
    print("All y elements occur after x elements")
else:
    print("All y elements don't occur after x elements")

Output

The list is :
[11, 25, 13, 11, 64, 25, 8, 9]
All y elements occur after x elements

How It Works

• A list is defined and displayed on the console.

• Two integer variables x and y are initialized.

• The index of the first occurrence of x is found using index().

• Using enumerate(), we iterate through the list to check each element.

• If any occurrence of y has an index less than x_index, the result is set to False.

• Based on the final result, the appropriate message is displayed.

Conclusion

Use enumerate() to compare indices of elements in a list. This approach efficiently checks positional relationships between specific values in the list.