Python：如何获取 itertools _grouper 的长度
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Python: How to get the length of itertools _grouper
提问by user1466679
I'm working with Python itertools and using groupby to sort a bunch of pairs by the last element. I've gotten it to sort and I can iterate through the groups just fine, but I would really love to be able to get the length of each group without having to iterate through each one, incrementing a counter.
我正在使用 Python itertools 并使用 groupby 按最后一个元素对一堆对进行排序。我已经把它排序了，我可以很好地遍历组，但我真的很想能够获得每个组的长度，而不必遍历每个组，增加一个计数器。
The project is cluster some data points. I'm working with pairs of (numpy.array, int) where the numpy array is a data point and the integer is a cluster label
该项目是对一些数据点进行聚类。我正在使用 (numpy.array, int) 对，其中 numpy 数组是一个数据点，整数是一个簇标签
Here's my relevant code:
这是我的相关代码：
data = sorted(data, key=lambda (point, cluster):cluster)
for cluster,clusterList in itertools.groupby(data, key=lambda (point, cluster):cluster):
if len(clusterList) < minLen:
On the last line: if len(clusterList) < minLen:, I get an error that
在最后一行：if len(clusterList) < minLen:，我收到一个错误
object of type 'itertools._grouper' has no len()
'itertools._grouper' 类型的对象没有 len()
I've looked up the operations available for _groupers, but can't find anything that seems to provide the length of a group.
我查找了可用于 的操作_groupers，但找不到任何似乎提供组长度的内容。
采纳答案by kindall
Just because you call it clusterListdoesn't make it a list! It's basically a lazy iterator, returning each item as it's needed. You can convert it to a list like this, though:
仅仅因为你调用它clusterList并不能使它成为一个列表！它基本上是一个惰性迭代器，根据需要返回每个项目。不过，您可以将其转换为这样的列表：
clusterList = list(clusterList)
Or do that and get its length in one step:
或者这样做并一步得到它的长度：
length = len(list(clusterList))
If you don't want to take up the memory of making it a list, you can do this instead:
如果您不想占用将其设为列表的内存，则可以这样做：
length = sum(1 for x in clusterList)
Be aware that the original iterator will be consumed entirely by either converting it to a list or using the sum()formulation.
请注意，原始迭代器将通过将其转换为列表或使用sum()公式来完全消耗。
回答by Brian Cain
clusterListis iterablebut it is not a list. This can be a little confusing sometimes. You can do a forloop over clusterListbut you can't do other list things over it (slice, len, etc).
clusterList是iterable但它不是list. 有时这可能有点令人困惑。您可以进行for循环，clusterList但不能对其进行其他列表操作（切片、len 等）。
Fix: assign the result of list(clusterList)to clusterList.
修复：将结果赋值list(clusterList)给clusterList。
