How to Extract Elements from a List Based on Known Indices?

Retrieving Multiple Elements from a List Based on Known Indices

To extract specific elements from a list knowing their indices, you can employ the following methods:

1. List Comprehension:

As you already demonstrated, list comprehensions provide a concise way to extract elements according to indices:

a = [-2, 1, 5, 3, 8, 5, 6]
b = [1, 2, 5]
c = [a[i] for i in b]

2. operator.itemgetter:

The itemgetter operator from the operator module allows you to retrieve elements based on a sequence of indices:

from operator import itemgetter
a = [-2, 1, 5, 3, 8, 5, 6]
b = [1, 2, 5]
print(itemgetter(*b)(a))
# Result: (1, 5, 5)

3. Numpy (if available):

If you have Numpy installed, you can leverage its array indexing capabilities:

import numpy as np
a = np.array([-2, 1, 5, 3, 8, 5, 6])
b = [1, 2, 5]
print(list(a[b]))
# Result: [1, 5, 5]

While all three methods can accomplish the task, the list comprehension approach is generally considered the most readable and concise. However, if you value speed or efficiency, itemgetter or Numpy might offer better performance.

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