Question

Write a function abs_list_rec(values) that takes as input a list of numbers called values, and that uses recursion to create and return a list containing the absolute values of the numbers in values. In other words, this function will do the same thing as the previous function, but it must use recursion instead of a list comprehension.

Answer 1

def abs_list_rec(values):
    # Base case
    if len(values)==0:
        return []
    # Recursive case
    else:
        # Making recursive call
        # abs_list_rec(values[:-1]) means making recursive call with values list except the last entry
        # [abs(values[-1])] means absolute value of last entry in list
        # + is used to append the list values
        return abs_list_rec(values[:-1]) + [abs(values[-1])]

# Testing
print(abs_list_rec([-2, 5, 8, -3]))