Which teacher has the most courses?

Question

Hey guys,

I keep getting this question wrong. I have a suspicion I'm not using the max() function right. It's supposed to call the largest item in an iterable but I keep getting the wrong answer.

I also wrote another function just trying to return the max of the dictionary but that is also incorrect.

Can you please help me to understand what is actually happening when I use the max function.
Am I using my if statement correctly? Should I be able to return the course associated with the largest course list?

Thanks!

teachers.py

# The dictionary will look something like:
# {'Andrew Chalkley': ['jQuery Basics', 'Node.js Basics'],
#  'Kenneth Love': ['Python Basics', 'Python Collections']}
#   
# Each key will be a Teacher and the value will be a list of courses.
#
# Your code goes below here.

def num_teachers(sing_arg):
    return len(sing_arg)

def num_courses(sing_arg):
    value = 0
    for course in sing_arg.values():
        value += len(course)
    return value

def courses(sing_arg):
    new_list = []
    for course in sing_arg.values():
        new_list.extend(course)  
    return new_list


# return the name of the teacher with the most courses
def most_courses(sing_arg):
    return max(sing_arg)


def most_courses(sing_arg):
    new_list = []
    for course in sing_arg.keys():
        new_list.append(sing_arg[course])
        if sing_arg[course] == max(new_list):
            return course

Answer 1 · 2018-07-20T07:36:33Z

July 20, 2018 7:36am

Let's walk through your current function.

def most_courses(sing_arg):
    new_list = []
    for course in sing_arg.keys():
        new_list.append(sing_arg[course])
        if sing_arg[course] == max(new_list):
            return course

First you assign new_list to an empty list. Then you append each list of courses in sing_arg to new_list. At this point, new_list is a list of lists with the courses.

new_list = [["Course1",  "Course2"], ["CourseA", "CourseB",  "CourseC"]]

Then you say, in effect:

if ["Course1",  "Course2"] == max([["Course1",  "Course2", "Course3"], ["CourseA", "CourseB"]]):
    return course

The problem is, that when you use max() on a list of a list of strings, the function will always return the list with the maximum alphabetical value for the first item of each list. Maximum alphabetical value means that "z" is greater than "a", because it's later in the alphabet. So, max(['a','b','c'], ['y', 'z']) will return ['y','z'] even though ['y','z'] is the shorter list, because 'y' has a higher alphabetical value than 'a'.

The point is, that your current approach can't work because you're comparing the alphabetical value of the course lists, instead of their lengths.

So we need a way to get the lengths of the course lists. Let's modify your function to do that:

def most_courses(sing_arg):
    new_list = []
    for course in sing_arg.keys():
        new_list.append(len(sing_arg[course]))
        if len(sing_arg[course]) == max(new_list):
            return course

Notice how I added len() before each sing_arg[course]. So now, new_list will contain the length of each course list, and our if statement will compare the length of our current course list against the maximum value in our new_list, which should be the length of the longest list of courses. But wait! Now we have another problem.

Since we are using the if statement inside of our for loop, in our first iteration for the loop, we will compare the length of the current list against the longest length in new_list, but at this point we've only been through our loop once, and we've only added one item to new_list, the length of our current course list!

So in effect, our conditional now says, if the length of the first course list equals the length of the first course list, return the first teacher's name. Since this will always be true, our function will now always return the name of the first teacher in our dictionary.

So, we need to wait until ALL the values are stored in new_list, THEN do our comparison, which means we'll need to loop through the dictionary twice. The first time through, we'll get the value of the longest course list, and the second time through, we'll compare the length of each course list against the maximum length, and return the name of the teacher if the values match.

Michael Hulet informed me that copypasta solutions are a no-no, so I will be good. Here's what we have so far, you can finish it no prob.

def most_courses(sing_arg):
    new_list = []
    for course in sing_arg.keys():
        new_list.append(len(sing_arg[course]))
    # loop through dictionary again, and return teacher with most courses

Just for fun, here's my solution:

def most_courses(courseList):
    max_courses = max(map(lambda x: len(x), courseList.values()))
    for key, value in courseList.items():
        #return teacher with most courses

Answer 2 · 2018-07-20T06:35:27Z

July 20, 2018 6:35am

First of all, I love that you're using built-in functions instead of re-implementing them yourself inline. That being said, while I managed to work out a one-liner solution combining a few of these functions that should theoretically work, it's very unnecessarily complicated and the challenge doesn't seem to like it for every test case, so you probably don't wanna use the max function here. When given a dictionary, the max function only compares the keys with each other, which is rarely useful.

Instead, what I'd do here is loop over the dictionary and keep track of which key corresponds to the longest list and return that after the end of the loop

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Anthony Lopez

Anthony Lopez

Which teacher has the most courses?

2 Answers

Kyle Knapp

Kyle Knapp

Michael Hulet

Michael Hulet

Kyle Knapp

Kyle Knapp

Anthony Lopez

Anthony Lopez

Kyle Knapp

Kyle Knapp

Michael Hulet

Michael Hulet

Anthony Lopez

Anthony Lopez