How do you remove a sublist if a certain element is not found at a specific position across all sublists?

In other words, if it's found that "f" is in the 4th position of the sublist, return that sublist, otherwise, exclude it if "f" is not found.

List = [['a','b','c','d','f'],['a','b','c','d','e'],['a','b','c','d','e'],['a','b','c','f','f'],['a','b']]

I have the following function which would work if all the sublists were the same size.

def Function(SM):
    return filter(lambda x: re.search("f",str(x[4])),List)

    IndexError: list index out of range

 Desired_List = [['a','b','c','d','f'],['a','b','c','f','f']]

I'm reluctant to use a for loop, because of the speed and efficiency costs. Are there any alternatives that are just as quick?

Solution

You can use list comprehension:

lst = [['a','b','c'], ['a','b','c','d','f'],['a','b','c','d','e'],['a','b','c','d','e'],['a','b','c','f','f'],['a','b']]
lst_desired = [l for l in lst if len(l) >= 5 and l[4] == "f"]
print lst_desired

Output

[['a', 'b', 'c', 'd', 'f'], ['a', 'b', 'c', 'f', 'f']]