python - 使用 python {census} 计算每个州的县数

Question

我在使用著名的 cenus.csv 计算县的数量时遇到了麻烦数据。

任务:统计每个州的县数。

面对比较(我认为)/请阅读下文？

我已经试过了:

df = pd.read_csv('census.csv')
dfd = df[:]['STNAME'].unique()  //Gives out names of state

serr = pd.Series(dfd)  // converting to series (from array)

在此之后，我尝试了两种方法:

1:

    df[df['STNAME'] == serr] **//ERROR: series length must match**

2:

i = 0
for name in serr:                        //This generate error 'Alabama'
    df['STNAME'] == name
    for i in serr:
        serr[i] == serr[name]
        print(serr[name].count)
        i+=1

请指导我；这些东西已经三天了。

Answer 1

使用 groupby 并使用 nunique 聚合 COUNTY:

In [1]: import pandas as pd

In [2]: df = pd.read_csv('census.csv')

In [3]: unique_counties = df.groupby('STNAME')['COUNTY'].nunique()

现在的结果

In [4]: unique_counties
Out[4]: 
STNAME
Alabama                  68
Alaska                   30
Arizona                  16
Arkansas                 76
California               59
Colorado                 65
Connecticut               9
Delaware                  4
District of Columbia      2
Florida                  68
Georgia                 160
Hawaii                    6
Idaho                    45
Illinois                103
Indiana                  93
Iowa                    100
Kansas                  106
Kentucky                121
Louisiana                65
Maine                    17
Maryland                 25
Massachusetts            15
Michigan                 84
Minnesota                88
Mississippi              83
Missouri                116
Montana                  57
Nebraska                 94
Nevada                   18
New Hampshire            11
New Jersey               22
New Mexico               34
New York                 63
North Carolina          101
North Dakota             54
Ohio                     89
Oklahoma                 78
Oregon                   37
Pennsylvania             68
Rhode Island              6
South Carolina           47
South Dakota             67
Tennessee                96
Texas                   255
Utah                     30
Vermont                  15
Virginia                134
Washington               40
West Virginia            56
Wisconsin                73
Wyoming                  24
Name: COUNTY, dtype: int64