Question

I work with python and I have a really basic question.
I an array of 1000 elements. I want to select 100 positions of this array.
I want to do something like

     selected_value=array[i for i in position_to_select]

How can I make this work?

Answer 1

Suppose you have the list arr, from which you want to select elements at positions 0, 4, 2:

>>> arr = [1, 2, 3, 4, 5, 6, 7]
>>> selected = [arr[i] for i in [0, 4, 2]]
>>> selected
[1, 5, 3]
>>> 

I think that the key difference with your original code sample is using arr[i] in the list comprehension. A list comprehension creates a new list. It is not used to index an existing list.