# How to extract elements from a list using indices in Python?

## Question:

If you have a list in python, and want to extract elements at indices 1, 2 and 5 into a new list, how would you do this?

This is how I did it, but I’m not very satisfied:

``````>>> a
[10, 11, 12, 13, 14, 15]
>>> [x for x in enumerate(a) if x in [1,2,5]]
[11, 12, 15]
``````

Is there a better way?

More in general, given a tuple of indices, how would you use this tuple to extract the corresponding elements from a list, even with duplication (e.g. tuple `(1,1,2,1,5)` produces `[11,11,12,11,15]`).

Perhaps use this:

``````[a[i] for i in (1,2,5)]
# [11, 12, 15]
``````

Try

``````numbers = range(10, 16)
indices = (1, 1, 2, 1, 5)

result = [numbers[i] for i in indices]
``````

Bounds checked:

`````` [a[index] for index in (1,2,5,20) if 0 <= index < len(a)]
# [11, 12, 15]
``````

I think you’re looking for this:

``````elements = [10, 11, 12, 13, 14, 15]
indices = (1,1,2,1,5)

result_list = [elements[i] for i in indices]
``````

Use Numpy direct array indexing, as in MATLAB, Julia, …

``````a = [10, 11, 12, 13, 14, 15];
s = [1, 2, 5] ;

import numpy as np
list(np.array(a)[s])
# [11, 12, 15]
``````

Better yet, just stay with Numpy arrays

``````a = np.array([10, 11, 12, 13, 14, 15])
a[s]
#array([11, 12, 15])
``````
Categories: questions Tags: ,
Answers are sorted by their score. The answer accepted by the question owner as the best is marked with
at the top-right corner.