How do you eliminate items from nested lists

Question

Given a list of ranked ballots and a list of candidates to eliminate, I need to return a new list of ranked ballots where all the candidates in the list of candidates to eliminate have been removed.

This is the code I've tried so far

import doctest def eliminate_candidate(ballots, to_eliminate): ''' (list, list) -> list >>> eliminate_candidate([['NDP', 'LIBERAL'], ['GREEN', 'NDP'], \ ['NDP', 'BLOC']], ['NDP', 'LIBERAL']) [[], ['GREEN'], ['BLOC']] >>> eliminate_candidate([], []) [] >>> eliminate_candidate([[]], []) [[]] ''' new_list = [] # Copy ballots onto new list for item in ballots: new_list.append(item) for item in new_list: for element in item: if element in to_eliminate: item.remove(element) return new_list

My first doctest is failing, giving me this output instead:

[['LIBERAL'], ['GREEN'], ['BLOC']]

igorkf · Accepted Answer · 2019-11-13 18:43:19Z

Using sets becomes pretty easy!

ballots = [['NDP', 'LIBERAL'], ['GREEN', 'NDP'], ['NDP', 'BLOC']] to_eliminate = ['NDP', 'LIBERAL'] result = [list(set(x) - set(to_eliminate)) for x in ballots] result [[], ['GREEN'], ['BLOC']]

Or:

result = [list(set(x).difference(to_eliminate)) for x in ballots] result [[], ['GREEN'], ['BLOC']]

quamrana · Accepted Answer · 2019-11-13 15:12:31Z

This is the function required. It searches through the sublists:

def eliminate_candidate(ballots, to_eliminate): return [[party for party in ballot if party not in to_eliminate] for ballot in ballots] ballots = [['NDP', 'LIBERAL'], ['GREEN', 'NDP'], ['NDP', 'BLOC']] to_eliminate = ['NDP', 'LIBERAL'] print(eliminate_candidate(ballots, to_eliminate))

Output:

[[], ['GREEN'], ['BLOC']]

User · Accepted Answer · 2019-11-13 15:17:23Z

1

ballots = [['NDP', 'LIBERAL'], ['GREEN', 'NDP'], ['NDP', 'BLOC']] to_eliminate = ['NDP', 'LIBERAL'] res = [[element for element in b if element not in to_eliminate] for b in ballots] print(res)

prints

[[], ['GREEN'], ['BLOC']]

edited Nov 13, 2019 at 15:17

answered Nov 13, 2019 at 15:00

User

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3 Comments

quamrana Over a year ago

Don't use list as the name of a variable!

quamrana Over a year ago

Your output seems to be different to the requirement stated by the OP.

quamrana Over a year ago

But that his output is not as the stated requirement.

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