Using Counter() in Python to build histogram?

For your data it is probably better to use a barchart instead of a histogram. Check out this code:

from collections import Counterimport numpy as npimport matplotlib.pyplot as pltlabels, values = zip(*Counter(['A','B','A','C','A','A']).items())indexes = np.arange(len(labels))width = 1plt.bar(indexes, values, width)plt.xticks(indexes + width * 0.5, labels)plt.show()

Result:

You can write some really concise code to do this using pandas:

    import numpy as np    from pandas import Series        sample = np.random.choice(['a', 'b'], size=10)        s = Series(sample)        In [29]: s    Out[29]:    0    a    1    b    2    b    3    b    4    a    5    b    6    b    7    b    8    b    9    a    dtype: object        vc = s.value_counts()        In [31]: vc    Out[31]:    b    7    a    3    dtype: int64        vc = vc.sort_index()        In [33]: vc    Out[33]:    a    3    b    7    dtype: int64        c.plot(kind='bar')

Resulting in:

Based on Igonato's answer I created a helper module 'plot' with a class 'Plot'.

It has two functions hist() and barchart() two show Igonato's approach as well as using the matplotlib hist functionality directly as might haven been originally intended in the question.

The approach allows adding a title and lables with a given fontsize and displays the y-axis with a tick frequency of 1. You can also change the mode so that it will save the chart with the given title. There are close and debug options for convenience.

python unit test test_Plot.py

'''Created on 2020-07-05@author: wf'''import unittestfrom ptp.plot import Plotclass TestPlot(unittest.TestCase):    def setUp(self):        pass    def tearDown(self):        pass    def testPlot(self):        ''' test a plot based on a Counter '''        valueList=['A','B','A','C','A','A'];        plot=Plot(valueList,"barchart example",xlabel="Char",ylabel="frequency")        plot.barchart(mode='save')        plot.title="histogram example"        plot.debug=True        plot.hist(mode='save')                passif __name__ == "__main__":    #import sys;sys.argv = ['', 'Test.testName']    unittest.main()

Results:

debug output:

   value  list:  ['A', 'B', 'A', 'C', 'A', 'A']counter  items:  dict_items([('A', 4), ('B', 1), ('C', 1)])counter values:  dict_values([4, 1, 1])counter   keys:  dict_keys(['A', 'B', 'C'])

plot.py

    '''Created on 2020-07-05@author: wf'''import matplotlib.pyplot as pltfrom collections import Counterimport numpy as npimport osclass Plot(object):    '''    create Plot based on counters    see https://stackoverflow.com/questions/19198920/using-counter-in-python-to-build-histogram    '''    def __init__(self, valueList,title,xlabel=None,ylabel=None,fontsize=12,plotdir=None,debug=False):        '''        Constructor        '''        self.counter=Counter(valueList)        self.valueList=valueList        self.title=title        self.xlabel=xlabel        self.ylabel=ylabel        self.fontsize=fontsize        self.debug=debug        path=os.path.dirname(__file__)        if plotdir is not None:            self.plotdir=plotdir        else:            self.plotdir=path+"/../plots/"            os.makedirs(self.plotdir,exist_ok=True)                def titleMe(self):                plt.title(self.title, fontsize=self.fontsize)        if self.xlabel is not None:            plt.xlabel(self.xlabel)        if self.ylabel is not None:                plt.ylabel(self.ylabel)                def showMe(self,mode='show',close=True):        ''' show me in the given mode '''        if mode=="show":            plt.show()         else:            plt.savefig(self.plotdir+self.title+".jpg")        if close:                plt.close()                    def barchart(self,mode='show'):        ''' barchart based histogram for the given counter '''        labels, values = zip(*self.counter.items())        indexes = np.arange(len(labels))        width = 1        self.titleMe()        plt.bar(indexes, values, width)        plt.xticks(indexes + width * 0.5, labels)        plt.yticks(np.arange(1,max(values)+1,step=1))        self.showMe(mode)            def showDebug(self):            print("   value  list: ",self.valueList)        print("counter  items: ",self.counter.items())        print("counter values: ",self.counter.values())        print("counter   keys: ",self.counter.keys())            def hist(self,mode="show"):        ''' create histogram for the given counter '''        if self.debug:            self.showDebug()        self.titleMe()        # see https://stackoverflow.com/a/2162045/1497139        plt.hist(self.valueList,bins=len(self.counter.keys()))        self.showMe(mode)        pass