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:
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# 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:
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[9, 7, 6] |
Example – nlargest() invoked with a comparison key function:
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# 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:
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City3 City5 City1 |