[collections] Make frequency table automatically

1. What is the collections library?

The Python library collections implements specialized container datatypes providing alternatives to Python's general purpose built in containers, dict, list, set, and tuple.

 

The Counter method provide dict subclass for counting hashable objects. When we pass a string or list to the Counter constructor as a factor, an object is returned that tells us how many times each character appears in the string or list.

 

The Counter class in the collections module extends Python's basic data structure, dictonary, so we can reuse the API provided by the dictionary as it is.

 

2. How to use Counter?

Step 1 : Import Library

from collections import Counter

 

Step 2 : Put the input data into method

counter = Counter(["A", "B", "A"])

 

Step 3 : Check the result stored in variable

counter
# result will be same as following : 
# Coutner({"A" : 2, "B" : 1})

 

3. Compare two ways of making frequency table

We can also make frequency table using dictionary. To make frequency table with dictionary, we increment value by 1 when we meet same value.

 

def freq_fueltype1(): 
    # Make empty dictionary table 
    fuel_freq = {} 
    
    # Extract fueltype from data and make frequency 
    fuel_idx = Cars_header.index('fueltype')
    for rows in Cars_rows: 
        fueltype = rows[fuel_idx] 
        
        if fueltype not in fuel_freq: 
            fuel_freq[fueltype] = 1
        else : 
            fuel_freq[fueltype] += 1
            
    return fuel_freq

def freq_fueltype2(): 
    from collections import Counter
    fuel_idx = Cars_header.index('fueltype')
    fueltype = [row[fuel_idx] for row in Cars_rows]
    fuel_freq = Counter(fueltype)
    
    return fuel_freq

def make_table_from_dict(table_): 
    from beautifultable import BeautifulTable
    table = BeautifulTable(maxwidth = 130) 
    table.column_headers = ['fuel_type', 'counts']
    for key, value in table_.items(): 
        table.append_row([key, value])
    print(table)
    
# Make frequency table using dictionary
make_table_from_dict(freq_fueltype1())

# Make frequency table using Counter method 
make_table_from_dict(freq_fueltype2())

 

We can find that freq_fueltype2 works well in make_table_from_dict function. It's because the Counter class in the collections module extends Python's basic data structure, dictonary.

 

 

Source from : https://docs.python.org/3/library/collections.html