Finding the index of elements based on a condition using python list comprehension

Question

The following Python code appears to be very long winded when coming from a Matlab background

>>> a = [1, 2, 3, 1, 2, 3]
>>> [index for ind         


        

Answer 1

• In Python, you wouldn't use indexes for this at all, but just deal with the values—[value for value in a if value > 2]. Usually dealing with indexes means you're not doing something the best way.

• If you do need an API similar to Matlab's, you would use numpy, a package for multidimensional arrays and numerical math in Python which is heavily inspired by Matlab. You would be using a numpy array instead of a list.

  >>> import numpy
  >>> a = numpy.array([1, 2, 3, 1, 2, 3])
  >>> a
  array([1, 2, 3, 1, 2, 3])
  >>> numpy.where(a > 2)
  (array([2, 5]),)
  >>> a > 2
  array([False, False,  True, False, False,  True], dtype=bool)
  >>> a[numpy.where(a > 2)]
  array([3, 3])
  >>> a[a > 2]
  array([3, 3])