基于多个参数的切片列表

Question

我曾多次发过类似的问题，但都被关闭了，或者被转到另一个没有回答我问题的帖子。我希望这次这个帖子能留下来。

我有一个美国人口普查数据的DF。我把各州与其对应的县进行了分组。还有另一栏，人口从高到低排序。我唯一想做的是把它切成片，这样我只得到每个州的三个人口最多的县。最后的结果应该是根据三个人口最多的县来显示三个人口最多的州。

这是到目前为止我的代码。

def answer_six():
    cdf = census_df[census_df['SUMLEV'] == 50]
    columns_to_keep = ['STNAME', 'CTYNAME', 'CENSUS2010POP']
    cdf = cdf[columns_to_keep]
    cdf = cdf.sort_values('CENSUS2010POP', ascending=False)
    cdf = cdf.groupby('STNAME')
    cdf = cdf.apply(pd.DataFrame.sort_values, 'CENSUS2010POP', ascending=False).head(100)
#    cdf = [i for i in cdf['STNAME'][:3] if all(cdf['STNAME']) == all(cdf['STNAME'])]
    return cdf
answer_six()

这是我的数据样本

    STNAME  CTYNAME           CENSUS2010POP             
37  Alabama Jefferson County    658466
49  Alabama Mobile County   412992
45  Alabama Madison County  334811
51  Alabama Montgomery County   229363
59  Alabama Shelby County   195085
63  Alabama Tuscaloosa County   194656
2   Alabama Baldwin County  182265
41  Alabama Lee County  140247
52  Alabama Morgan County   119490
8   Alabama Calhoun County  118572
28  Alabama Etowah County   104430
35  Alabama Houston County  101547
48  Alabama Marshall County 93019
39  Alabama Lauderdale County   92709
58  Alabama St. Clair County    83593
42  Alabama Limestone County    82782
61  Alabama Talladega County    82291
22  Alabama Cullman County  80406
26  Alabama Elmore County   79303
25  Alabama DeKalb County   71109
64  Alabama Walker County   67023
5   Alabama Blount County   57322
1   Alabama Autauga County  54571
17  Alabama Colbert County  54428
36  Alabama Jackson County  53227
57  Alabama Russell County  52947
23  Alabama Dale County 50251
16  Alabama Coffee County   49948
24  Alabama Dallas County   43820
11  Alabama Chilton County  43643
... ... ... ... ...
80  Alaska  Kenai Peninsula Borough 55400
79  Alaska  Juneau City and Borough 31275
72  Alaska  Bethel Census Area  17013

Answer 1

我猜你要找的是 cdf.groupby('STNAME').head(3) 在你整理好cdf后？

P.S.也许你的问题一直被关闭是因为重复的问题吧，比如。Pandas在每组中得到最多的n条记录。