Python removing specific duplicates from a list

Question

I want to remove specific duplicates from a list. With Perl I would do the task with this code:

my @list = ( 'a1', 'a1', 'b1', 'b1' );

my %seen;
@list = grep( !/a\d/ || !$seen{ $_ }++, @list );

and the wanted result would be this:

@list = ( 'a1', 'b1', 'b1' );

How could I do this in Python 3 using regular expression and list comprehension. Thanks.

Answer 1

You can use itertools.chain and groupby :

>>> list(chain(*[[i[0]] if 'a1' in i else i for i in [list(g) for _,g in groupby(sorted(l))]]))
['a1', 'b1', 'b1']

and if you just want to use regex you can concatenate the elements the n use re.sub , but note that it works for this special case ! that , is the delimiter ! :

>>> l =['a1', 'a1', 'b1', 'b1']
>>> re.sub(r'(a1,)+','a1,',','.join(sorted(l))).split(',')
['a1', 'b1', 'b1']

Answer 2

import re
from functools import reduce  # this import is not needed in python 2.*

l = ['a1', 'a1', 'b1', 'b1']

print reduce(lambda acc, el: acc if re.match(r'a\d', el) and el in acc else acc + [el], l, [])

Sorry, this is solution without list comprehensions. Is it strictly required?