pandas groupby:获取知道其ID的组的大小(来自.grouper.group_info [0]) [英] Pandas groupby: get size of a group knowing its id (from .grouper.group_info[0])
问题描述
在以下代码段中,data
是pandas.DataFrame
,indices
是data
的一组列.用groupby
对数据进行分组后,我对组的ID感兴趣,但仅对那些大小大于阈值(例如3)的ID感兴趣.
In the following snippet data
is a pandas.DataFrame
and indices
is a set of columns of the data
. After grouping the data with groupby
I am interested in the ids of the groups, but only those with a size greater than a threshold (say: 3).
group_ids=data.groupby(list(data.columns[list(indices)])).grouper.group_info[0]
现在,在知道该组的ID的情况下,我如何才能找到哪个组的大小大于或等于3?我只想要具有特定大小的群组ID.
Now, how can I find which group has a size greater than or equal 3 knowing the id of the group? I only want ids of groups with a certain size.
#TODO: filter out ids from group_ids which correspond to groups with sizes < 3
推荐答案
一种方法是使用 groupby
的rel ="noreferrer"> size
方法:
One way is to use the size
method of the groupby
:
g = data.groupby(...)
size = g.size()
size[size > 3]
例如,这里只有一组大小> 1的
For example, here there is only one group of size > 1:
In [11]: df = pd.DataFrame([[1, 2], [3, 4], [1,6]], columns=['A', 'B'])
In [12]: df
Out[12]:
A B
0 1 2
1 3 4
2 1 6
In [13]: g = df.groupby('A')
In [14]: size = g.size()
In [15]: size[size > 1]
Out[15]:
A
1 2
dtype: int64
如果您只想将DataFrame限制为大型组中的对象,则可以使用过滤器方法:
If you were interested in just restricting the DataFrame to those in large groups you could use the filter method:
In [21]: g.filter(lambda x: len(x) > 1)
Out[21]:
A B
0 1 2
2 1 6
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