Remove Negative Elements in List-Python
Last Updated :
11 Feb, 2025
The task of removing negative elements from a list in Python involves filtering out all values that are less than zero, leaving only non-negative numbers. Given a list of integers, the goal is to iterate through the elements, check for positivity and construct a new list containing only positive numbers. For example, if a = [5, 6, -3, -8, 9, 11, -12, 2], the resulting list after removing negative numbers would be [5, 6, 9, 11, 2].
Using list comprehension
List comprehension is the most concise and Pythonic way to filter out negative numbers. It iterates through the list, applying a condition (ele > 0) to include only positive values. This method is widely used due to its readability and efficiency in handling small to moderately large lists.
Python
a = [5, 6, -3, -8, 9, 11, -12, 2]
res = [ele for ele in a if ele > 0]
print(res)
Explanation: list comprehension iterates through each element, keeping only those greater than 0, and stores them in res.
Using filter()
filter() applies a boolean condition (lambda x: x > 0) to each element, returning an iterator with only positive numbers. It is a functional programming approach that enhances code clarity and efficiency, especially when working with built-in filtering methods.
Python
a = [5, 6, -3, -8, 9, 11, -12, 2]
res = list(filter(lambda x: x > 0, a))
print(res)
Explanation: filter() with a lambda function to retain only positive numbers from a, converting the result to a list.
compress() filters a list based on a predefined boolean mask ([x > 0 for x in a]). It is useful when working with complex filtering conditions or when a separate boolean mask needs to be used for multiple operations. While not as common as list comprehension, it is an optimized method for selective filtering.
Python
from itertools import compress
a = [5, 6, -3, -8, 9, 11, -12, 2]
mask = [x > 0 for x in a]
res = list(compress(a, mask))
print(res)
Explanation: itertools.compress() with a boolean mask to filter out negative numbers. The mask [x > 0 for x in a] marks positives as True and compress(a, mask) retains only those values.
Using numpy
NumPy provides an optimized, vectorized approach for filtering numerical data. Using a[a > 0] efficiently extracts positive elements without explicit loops. This method is ideal for large datasets, offering high-speed performance compared to traditional Python lists.
Python
import numpy as np
# Creating a NumPy array
a = np.array([5, 6, -3, -8, 9, 11, -12, 2])
# Creating a NumPy array
res = a[a > 0]
print(res.tolist()) # Convert back to list if needed
Explanation: This code selects only positive numbers from a using NumPy's indexing (a[a > 0]), which is faster than loops. The result is then converted into a list using .tolist().
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