Efficiently replace elements in array based on dictionary - NumPy / Python

Question

First, of all, my apologies if this has been answered elsewhere. All I could find were questions about replacing elements of a given value, not elements of multiple values.<

Answer 1

Given that you're using numpy arrays, I'd suggest you do a mapping using numpy too. Here's a vectorized approach using np.select:

mapping = {1:2, 5:3, 8:6}
keys, choices = list(zip(*mapping.items()))
# [(1, 5, 8), (2, 3, 6)]
# we can use broadcasting to obtain a 3x100x100
# array to use as condlist
conds = np.array(keys)[:,None,None]  == input_array
# use conds as arrays of conditions and the values 
# as choices
np.select(conds, choices)

array([[2, 2, 2, ..., 0, 0, 0],
       [2, 2, 2, ..., 0, 0, 0],
       [2, 2, 2, ..., 0, 0, 0],
       ...,
       [0, 0, 0, ..., 0, 0, 0],
       [0, 0, 0, ..., 0, 0, 0],
       [0, 0, 0, ..., 0, 0, 0]])