[Matplotlib] Bar 그래프와 예제 plt.bar()

 

 

 

matplotlib¶

 

matplotlib.pyplot 라이브러리 import

In [1]:

import matplotlib.pyplot as plt

 

Bar¶

• show how some quantity varies

In [10]:

plt.bar([1,3,0,10], [10,23,30,1])
plt.show()

 

 

width¶

• default = 0.8 (기본 0.8로 설정되어 있음)

In [11]:

plt.bar([1,2,3,4,5],[10,20,30,40,50], width=0.1)
plt.show()

 

 

Bar의 위치 변경¶

In [12]:

def make_chart_simple_bar_chart():
    movies = ["Annie Hall", "Ben-hur", "Casablanca", "Gandhi"]
    num_oscars = [5, 11, 3, 8]
    
    #left coordinates so that each bar is centered
    xs = [i + 0.5 for i, _ in enumerate(movies)]
    
    plt.bar(xs, num_oscars)
    plt.ylabel("# of Academy Awards")
    plt.xlabel("My Favorite Movies")
    plt.title("My Favorite Movies")
    
    plt.xticks([i for i,_ in enumerate(movies)], movies)
    
    plt.show()

make_chart_simple_bar_chart()

 

 

점수분포 Bar 예제¶

In [13]:

from collections import Counter

def make_chart_histogram():
    grades = [83, 95, 91, 87, 70, 0, 85, 82, 100, 67, 73, 77, 0]
    decile = lambda x: (x // 10) * 10  # 십분위로 나타내기(1의 자리 버리기)
    histogram = Counter(decile(grade) for grade in grades)
#     print(decile)
#     print(histogram)
    
    #left coordinates so that each bar is centered
    plt.bar([x+5 for x in histogram.keys()], histogram.values(), width = 0.8)
    
    plt.axis([-5, 105, 0, 5])
    
    plt.xticks([10 * i for i in range(11)])
    plt.xlabel("Decile")
    plt.ylabel("# of students")
    plt.title("Distribution of Exam 1 Grades")
    plt.show()
make_chart_histogram()

 

 

misleading at bar chart¶

• bar 그래프에서 일어날 수 있는 잘못된 chart 의 예

In [14]:

'''인자로 True 를 받으면 y축의 값을 차이가 별로 없게 확대(499~506)
False 를 받으면 정상적으로 y축의 값을 0~505 로 설정'''
def make_chart_misleading_y_axis(mislead=True):
    
    mentions = [500, 505]
    years = [2013, 2014]
    
    plt.bar([2012.6,2013.6], mentions, 0.8)
    plt.xticks(years)
    plt.ylabel("# of times I heard someone say 'data science'")
    
    if mislead:
        #misleading y-axis only shows the part above 500
        plt.axis([2012.5, 2014.5, 499, 506]) #bad
        plt.title("misleading (Huge difference)")
    else: #실제로는 5밖에 차이 안남
        plt.axis([2012.5, 2014.5, 0, 550]) #good
        plt.title("just 5 difference")
    plt.show()

In [15]:

make_chart_misleading_y_axis(True)

 

In [16]:

make_chart_misleading_y_axis(False)