Python: Select subset from list based on index set

Question

I have several lists having all the same number of entries (each specifying an object property):

property_a = [545., 656., 5.4, 33.]
property_b = [ 1.2,  1.3         


        

Answer 1

Matlab and Scilab languages offer a simpler and more elegant syntax than Python for the question you're asking, so I think the best you can do is to mimic Matlab/Scilab by using the Numpy package in Python. By doing this the solution to your problem is very concise and elegant:

from numpy import *
property_a = array([545., 656., 5.4, 33.])
property_b = array([ 1.2,  1.3, 2.3, 0.3])
good_objects = [True, False, False, True]
good_indices = [0, 3]
property_asel = property_a[good_objects]
property_bsel = property_b[good_indices]

Numpy tries to mimic Matlab/Scilab but it comes at a cost: you need to declare every list with the keyword "array", something which will overload your script (this problem doesn't exist with Matlab/Scilab). Note that this solution is restricted to arrays of number, which is the case in your example.