Nlargest Function Of Heapq Module In Python

Overview:

  • The nlargest() function of the Python module heapq returns the specified number of largest elements from a Python iterable like a list, tuple and others.
  • The function nlargest() can also be passed a key function that returns a comparison key to be used in the sorting.

Example:

# Example Python program that finds the largest n elements

# from a Python iterable

import heapq

 

iterable = [6,1,7,9,3,5,4]

selectCount = 3

largests = heapq.nlargest(selectCount, iterable)

print(largests)

 

 

Output:

[9, 7, 6]

 

Example – nlargest() invoked with a comparison key function:

# Example Python program that finds the largest n elements

# from a Python iterable

import heapq

 

# Define a function that returns a comparison key for city objects

def sortkey(city):

    return city.population

 

# Define a City class

class City:

    def __init__(self, id, name, population):

        self.id = id

        self.name = name

        self.population = population

 

    def __str__(self):        

        return self.name

 

# Create instances of City class

c1 = City(1, "City1", 1500)       

c2 = City(2, "City2", 1100)      

c3 = City(3, "City3", 1700)        

c4 = City(4, "City4", 1200)       

c5 = City(5, "City5", 1600)        

 

# Make a list of City instances

cities = [c1, c2, c3, c4, c5]

 

# Find three most populated cities

mostPopulated = heapq.nlargest(3, cities, key = sortkey)

 

# Print three most populated cities

for city in mostPopulated:

    print(city)

 

Output:

City3

City5

City1


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