python map function (+ lambda) involving conditionals (if)

Question

I'm curious if it's possible to do something with the map()function that I can do via list comprehension.

For ex, take this list comp:

example_list = [x*2 for x in range(5) if x*2/6. != 1]

obviously, this gives me [0, 2, 4, 8].

How do I make the equivalent using the map() function? Doing this gives me a syntax error.

example_map = map(lambda x:x*2 if x*2/6. != 1, range(5))

Just trying to get a better understanding of how to use this function.

Answer 1

You'll have to wrap the map around a filter around the list:

example_map = map(lambda x: x*2, filter(lambda x: x*2/6. != 1, range(5)))

Answer 2

Alternatively, you could filter your map rather than maping your filter.

example_map = filter(lambda x: x/6. != 1, map(lambda x: x*2, range(5)))

Just remember that you're now filtering the RESULT rather than the original (i.e. lambda x: x/6. != 1 instead of lambda x: x*2/6. != 1 since x is already doubled from the map)

Heck if you really want, you could kind of throw it all together with a conditional expression

example_map = map(lambda x: x*2 if x*2/6. != 1 else None, range(5))

But it'll leave you with [0, 2, 4, None, 8]. filter(None, example_map) will drop the Nones and leave you [0, 2, 4, 8] as expected.