Overview:
- The nsmallest() method of the Python module heapify returns the specified number of smallest elements from an iterable in sorted order.
- A key function can be passed as an argument to the nsmallest() function. The key function accepts one parameter and returns the comparison key to be used in the sorting process.
- Using a key function helps sorting records based on a specific field where elements are actually objects or records with several attributes or fields.
Example:
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# Example Python program that uses heapq.nsmallest() # function to find the n smallest elements from an iterable import heapq
select = 4 elements = (2, 9, 17, 11, 6, 16, 8) smallests = heapq.nsmallest(select, elements) print(smallests) |
Output:
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[2, 6, 8, 9] |
Example – Finding ‘n’ smallest elements using the key function:
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# Example Python program that uses heapq.nsmallest() # along with a function that produces comparison keys import heapq
# Key function returning the total scores def total(result): return result.math + result.physics + result.physics + result.physics
# Class defining Objects representing records of exam results class ExamResult: def __init__(self, id, math, physics, chemistry, biology): self.id = id self.math = math self.physics = physics self.chemistry = chemistry self.biology = biology
def __str__(self): return "%d"%self.id
# ExamResult objects r1 = ExamResult(11, 55, 60, 75, 65) r2 = ExamResult(12,95, 80, 76, 78) r3 = ExamResult(13, 50, 65, 60, 85) r4 = ExamResult(14, 55, 57, 50, 75)
# Find the lowest total scores lowest = heapq.nsmallest(2, [r1, r2, r3, r4], key=total) for result in lowest: print(result) |
Output:
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14 11 |