Question

该作业由我的教授写在文档字符串中：

def evaluateBallot (voterPreferences, candidates):
    """
    Using voterPreferences (a dict associating each voter with a list of
      candidate names ordered from highest to lowest preference) and
      candidates(a set of candidates still remaining in the election),
      returns the vote distribution: a dict associating the name of each
      candidate in the election to the number of votes that they received
    >>> result = evaluateBallot(dict(x=['a','b','c'], y=['a','c','b'],z= ['c','a','b']),set(['b','c'])) 
    >>> (result['b'],result['c'])
    (1, 2)
    """

    d ={}
    for candidate in candidates:
       d[candidate] = 0
    for voterPreference in voterPreferences:
       if candidate == voterPreference[0]:
          d[candidate] += 1
    return d

当我运行我编写的代码时，每次候选人是选民的首选时，字典都不会更新+1。我觉得错误在我的if语句中，但我不确定它到底是什么？

Answer 1

如果数据与您在评论中描述的数据相似，那么我认为

for voterPreference in voterPreferences:

应改为

for voterPreference in voterPreferences.values():

因为你想让voterPreference成为['a'，'b'，'c']而不是'x'。

P.S。我不太明白为什么输出应该是b = 1和c = 2。如果在候选人中不存在而在voterPreferences中存在，你想如何处理？无视它？如果是这样，您需要在方法中使用更多逻辑来处理这个问题。

其他

根据您的意见，在计算最终结果时，似乎应忽略非候选人：

def evaluateBallot(voterPreferences, candidates): d = {} voterPrefCandOnly = [] # Just use list since we don't care about who voted # Remove votes for non-candidates for voterPref in voterPreferences.values(): filtered = filter(lambda x: x in cand, voterPref) voterPrefCandOnly.append(filtered) # Calculate the result for voting for candidate in candidates: d[candidate] = 0 for voterPref in voterPrefCandOnly: if candidate == voterPref[0]: d[candidate] += 1 return d voterPref = dict(x=['a','b','c'], y=['a','c','b'], z=['c','a','b']) cand = set(['b','c']) result = evaluateBallot(voterPref, cand) print (result['b'], result['c']) # (1, 2)

Answer 2

我认为这项任务假定读者理所当然地进行了一种特定的径流投票。因此，老师似乎也暗示“每个人只投一票，而那个投票将发给他们评价最高的候选人candidates”

这是一个完整的答案，您可以在完成后检查您的工作，或者您是否长时间陷入困境，或者希望检查您的假设：

def evaluateBallot(voterPreferences, candidates):
    """
       . . . 
    """
    votes = collections.Counter()  # or collections.defaultdict(lambda: 0)

    for voter,prefOrdering in voterPreferences.items():            
        for desiredCandidate in prefOrdering: # go through each person's preference list
            if desiredCandidate in candidates: # if candidate is still in the running                    
                # then this person votes for that candidate
                votes[desiredCandidate] += 1
                break
        # it is possible that the person casts no votes

    return dict(votes)

Answer 3

for candidate in candidates:
   d[candidate] = 0

此循环结束后，candidate具有candidates中最后一位候选人的值。

for voterPreference in voterPreferences:
   if candidate == voterPreference[0]:
      d[candidate] += 1

在此循环中，我们使用剩余的candidate值，并仅更新该候选人的投票。

我假设您要做的是检查voterPreference[0]是否是有效候选人。为此，我们可以检查voterPreference[0] in是否为现有d，并相应更新：

for voterPreference in voterPreferences:
   if voterPreference[0] in d:
      d[voterPreference[0]] += 1

我们可以通过使用voterPreference的元组解包来简化此操作，如果我们知道它有多长项，或者将voterPreference[0]分配给另一个变量。此外，您的3空格缩进是非标准的;请考虑切换到4：）

在Python中更新dict值

3 个答案: