Removing an element from a list based on a predicate

Question

I want to remove an element from list, such that the element contains \'X\' or \'N\'. I have to apply for a large genome. Here is an example:

Answer 1

1. filter(lambda x: 'N' not in x or 'X' not in x, your_list)
2. your_list = [x for x in your_list if 'N' not in x or 'X' not in x]

Answer 2

I like gnibbler’s memoization approach a lot. Either method using memoization should be identically fast in the big picture on large data sets, as the memo dictionary should quickly be filled and the actual test should be rarely performed. With this in mind, we should be able to improve the performance even more for large data sets. (This comes at some cost for very small ones, but who cares about those?) The following code only has to look up an item in the memo dict once when it is present, instead of twice (once to determine membership, another to extract the value).

codon = ['AAT', 'XAC', 'ANT', 'TTA']
def pred(s,memo={}):
    try:
        return memo[s]
    except KeyError:
        memo[s] = not any(y in s for y in "XN")
    return memo[s]

filtered = filter(pred, codon)

As I said, this should be noticeably faster when the genome is large (or at least not extremely small).

If you don’t want to duplicate the list, but just iterate over the filtered list, do something like:

for item in (item for item in codon if pred):
    do_something(item)

Answer 3

There is also the method of doing it using filter

    lst = filter(lambda x: 'X' not in x and 'N' not in x, list)