#!/usr/bin/env python
# coding: utf-8

# # Chapter 16 Exam Statistics 
# 
# <img align="left" src="https://i.imgur.com/lnc0qMV.png" />

# In[2]:


# 01 성적을 살펴봅시다!

grades = [100, 100, 90, 40, 80, 100, 85, 70, 90, 65, 90, 85, 50.5]
print ("Grades:", grades)


# In[4]:


# 02 성적 출력하기

grades = [100, 100, 90, 40, 80, 100, 85, 70, 90, 65, 90, 85, 50.5]

def print_grades(grades):
    for e in grades:
        print (e)

print_grades(grades)


# In[5]:


# 03 리뷰

print ("Let's compute some stats!")


# In[7]:


# 04 점수의 총합

grades = [100, 100, 90, 40, 80, 100, 85, 70, 90, 65, 90, 85, 50.5]

def grades_sum(scores):
    total = 0
    for score in scores:
        total += score
    return total

print (grades_sum(grades))


# In[9]:


# 05 평균값 계산하기

grades = [100, 100, 90, 40, 80, 100, 85, 70, 90, 65, 90, 85, 50.5]

def grades_sum(scores):
    total = 0
    for score in scores:
        total += score
    return total

def grades_average(grades):
    num = len(grades)
    return grades_sum(grades) * 1.0 / num

print (grades_average(grades))


# In[10]:


# 06 리뷰

print ("Time to conquer the variance!")


# In[12]:


# 07 분산

grades = [100, 100, 90, 40, 80, 100, 85, 70, 90, 65, 90, 85, 50.5]

def print_grades(grades):
    for grade in grades:
        print (grade)

def grades_sum(grades):
    total = 0
    for grade in grades:
        total += grade
    return (total)

def grades_average(grades):
    sum_of_grades = grades_sum(grades)
    average = sum_of_grades * 1.0/ len(grades)
    return (average)

def grades_variance(grades, average):
    variance = 0.0
    for grade in grades:
        variance += (grade - average) ** 2
    return variance / len(grades)

print (grades_variance(grades, grades_average(grades)))

# 분산(variance)은 편차 제곱의 평균
# 편차(deviation)는 평균과 차이 (즉, 평균에서 얼마나 떨어져 있는지 값)


# In[18]:


# 08 표준 편차


grades = [100, 100, 90, 40, 80, 100, 85, 70, 90, 65, 90, 85, 50.5]

def print_grades(grades):
    for grade in grades:
        print (grade)

def grades_sum(grades):
    total = 0
    for grade in grades:
        total += grade
    return (total)

def grades_average(grades):
    sum_of_grades = grades_sum(grades)
    average = sum_of_grades * 1.0/ len(grades)
    return (average)

def grades_variance(grades, average):
    variance = 0.0
    for grade in grades:
        variance += (grade - average) ** 2
    return variance / len(grades)

def grades_std_deviation(variance):
    return variance ** 0.5

print (grades_std_deviation(grades_variance(grades, grades_average(grades))))


# 표준편차(SD, standard deviation): 분산(variance)의 제곱근


# In[19]:


# 09 리뷰

grades = [100, 100, 90, 40, 80, 100, 85, 70, 90, 65, 90, 85, 50.5]

def print_grades(grades):
    for grade in grades:
        print (grade)

def grades_sum(grades):
    total = 0
    for grade in grades:
        total += grade
    return total

def grades_average(grades):
    sum_of_grades = grades_sum(grades)
    average = sum_of_grades * 1.0/ len(grades)
    return average

def grades_variance(grades, average):
    variance = 0.0
    for grade in grades:
        variance += (grade - average) ** 2
    return variance / len(grades)

def grades_std_deviation(variance):
    return variance ** 0.5

print_grades(grades)
print (grades_sum(grades))
print (grades_average(grades))
print (grades_variance(grades, grades_average(grades)))
print (grades_std_deviation(grades_variance(grades, grades_average(grades))))


grades = [100, 100, 90, 40, 80, 100, 85, 70, 90, 65, 90, 85, 50.5]
print ("Grades:", grades)