# Write a function call most_common that
# accepts the file name to be read.
# The file contains courses students will take spring 2019.
# The function then returns the most common course
# (be careful, the problem asks for the course, not the number
# of students who will enroll in the course)

def most_common(filename):
    course_dict = {}

    infile = open(filename, 'r')
    list_of_lines = infile.read().split('\n')
    for line in list_of_lines:
        columns = line.split(',')

         # skip column 0 since it is not course name
        for i in range(1, len(columns)):
            # by default, python will look in keys of dict
            if columns[i] in course_dict:   # similar to checking in course_dict.keys()
                course_dict[columns[i]] += 1   # increment value associate with key = columns[i]
            else:
                course_dict[columns[i]] = 1    # add a key-value pair to dict where key is columns[i]

    # done with file, don't forget to close it
    infile.close()

    # Iterate over a course_dict and find course (key) with the highest value
    # Don't use max(course_dict) since it will return
    # max of course_dict's key, not the value.

    max_enroll = 0
    common_course = ''
    for k,v in course_dict.items():
        if max_enroll < v:
            max_enroll = v
            common_course = k

    return common_course

print('most_common ---', most_common('course-s19.csv'))


# Create a second (modified) version of the
# most_common function that returns a dictionary,
# where the key is course and the value is
# the number of students who will take that course

def most_common2(filename):

    course_dict = {}

    infile = open(filename, 'r')
    list_of_lines = infile.read().split('\n')
    for line in list_of_lines:
        columns = line.split(',')

         # skip column 0 since it is not course name
        for i in range(1, len(columns)):
            # by default, python will look in keys of dict
            if columns[i] in course_dict:   # similar to checking in course_dict.keys()
                course_dict[columns[i]] += 1   # increment value associate with key = columns[i]
            else:
                course_dict[columns[i]] = 1    # add a key-value pair to dict where key is columns[i]

    # done with file, don't forget to close it
    infile.close()

    return course_dict

print('most_common2 ---', most_common2('course-s19.csv'))


# Create another (modified) version of the
# most_common2 function that, print a dictionary (instead of return)
# in the following format:
#    5 students will take CS1
#    2 students will take CS2
#    ...
# (don't worry about the order, just focus on using key and value
# and format the output)

def most_common3(filename):

    course_dict = {}

    infile = open(filename, 'r')
    list_of_lines = infile.read().split('\n')
    for line in list_of_lines:
        columns = line.split(',')

         # skip column 0 since it is not course name
        for i in range(1, len(columns)):
            # by default, python will look in keys of dict
            if columns[i] in course_dict:   # similar to checking in course_dict.keys()
                course_dict[columns[i]] += 1   # increment value associate with key = columns[i]
            else:
                course_dict[columns[i]] = 1    # add a key-value pair to dict where key is columns[i]

    # done with file, don't forget to close it
    infile.close()

    for k,v in course_dict.items():
        print(v, 'students will take', k)

# print('most_common3 ---', most_common3('course-s19.csv'))   # since most_common3 doesn't return anything (i.e., None), print will show None
print('most_common3 ---')
most_common3('course-s19.csv')