change array column values without loop

[DeaD_EyE]

List Comprehension with conditional expression:

data = [0.16, 0, 0, 0.65, 0.17]
result = [x * 2 if x < 0.5 else x for x in data]

If you use numpy or pandas, you're using implicit for-loops. But in the numpy case, the for-loop is written in C. Operations on a numpy arrays are much faster than looping and doing the same in Python. To know how you can do broadcast operations with Python, is useful.