So I'm trying to learn Numpy and I cannot understand how this block of code is giving the output it is:
arr = array([1,2,3,4,5,6,7,8,9,10])
arr[arr>5]
Output :
array([6,7,8,9,10])
I do know that actually an array of boolean values is returned by arr>5 but I just can't understand how that boolean array when passed to arr[] gives the specified output.
Help Appreciated.
>>> import numpy as np
>>> a = np.array([1, 2, 3, 4, 5, 6, 7, 8, 9, 10])
>>> a
array([ 1, 2, 3, 4, 5, 6, 7, 8, 9, 10])
As you already said, a > 5 results in an array of boolean values:
>>> mask = a > 5
>>> mask
array([False, False, False, False, False, True, True, True, True,
True])
This can be interpreted as a mask. Similar to the way you can access single elements, for example the first element, with
>>> a[0]
1
You can access specific elements by using index arrays through this mask:
>>> a[mask]
array([ 6, 7, 8, 9, 10])
1, 2, 3, 4, 5 don't appear because the first 5 elements of mask are False. The rest is True and therefore 6, 7, 8, 9, 10 are shown.
