Question

Imagine a list that has random words:

words = ['elephant', 'dog', 'blue', 'sam', 'white', 'red', 'sun', 'moon']

And I want to remove all but the following words (like a whitelist):

colors = ['red', 'green', 'blue', 'orange', 'white']

And I want to produce the following list (order matters):

filtered = ['blue', 'white', 'red']

I’ve thought about something like this (which works fine):

filtered = filter (lambda a: a == 'red' or a == 'green' or a == 'blue' or a == 'orange' or a == 'white', words)

But is this really the best / most efficient way?

Answer 1

If you want to keep order and efficiently filter out non-colors, create a set of colors, so that in checking is faster and then you can just go thru all words and filter out non-colors

words = ['elephant', 'dog', 'blue', 'sam', 'white', 'red', 'sun', 'moon']
colors = set(['red', 'green', 'blue', 'orange', 'white'])
print [word for word in words if word in colors]

output:

['blue', 'white', 'red']