如何获取熊猫中每对唯一列的列值计数？

Question

我有下面给出的数据

data = [(datetime.datetime(2020, 12, 21, 6, 50, 14, 955551), 'blr', 'del', 'medium'), (datetime.datetime(2020, 12, 21, 7, 6, 0, 242578), 'lon', 'del', 'medium'), (datetime.datetime(2020, 12, 21, 7, 16, 30, 260692), 'lon', 'del', 'medium'), (datetime.datetime(2020, 12, 21, 7, 18, 15, 333229), 'lon', 'del', 'medium'), (datetime.datetime(2020, 12, 21, 7, 29, 0, 839566), 'lon', 'del', 'medium'), (datetime.datetime(2020, 12, 21, 7, 37, 45, 211979), 'lon', 'del', 'low'), (datetime.datetime(2020, 12, 21, 7, 41, 15, 211376), 'lon', 'del', 'medium'), (datetime.datetime(2020, 12, 21, 7, 48, 16, 26287), 'lon', 'del', 'low'), (datetime.datetime(2020, 12, 21, 7, 55, 17, 248074), 'ny', 'del', 'low'), (datetime.datetime(2020, 12, 21, 7, 57, 2, 55666), 'lon', 'del', 'medium'), (datetime.datetime(2020, 12, 21, 8, 4, 2, 319699), 'lon', 'del', 'low'), (datetime.datetime(2020, 12, 21, 8, 25, 5, 982621), 'ny', 'del', 'medium'), (datetime.datetime(2020, 12, 21, 8, 26, 50, 997280), 'lon', 'del', 'medium'), (datetime.datetime(2020, 12, 21, 8, 39, 7, 14287), 'lon', 'del', 'medium'), (datetime.datetime(2020, 12, 21, 8, 47, 51, 810956), 'lon', 'del', 'medium'), (datetime.datetime(2020, 12, 21, 9, 37, 23, 99922), 'ny', 'del', 'low')]

这就是我在 pandas 中加载它的方式

import pandas as pd
import datetime

df = pd.DataFrame(data)
df.columns = ["date", "start", "end", "type"]
df.set_index('date', inplace=True)

现在我可以通过执行类似的操作来获取所有具有特定类型的行，例如 medium

print(df[df.values == 'medium'])

现在我想知道start 和end 的每一对唯一对，medium 类型的计数是多少？基本上我想要类似的东西

blr del 1
lon del 9
ny  del 1

但我不知道我怎样才能得到它。如何做到这一点？

Answer 1

使用GroupBy.size 指定列进行测试：

s1 = df[df.values == 'medium'].groupby(['start','end']).size()
print (s1)
start  end
blr    del    1
lon    del    9
ny     del    1
dtype: int64

或者如果还想要type的所有组合：

print(df.groupby(['type','start','end']).size())
type    start  end
low     lon    del    3
        ny     del    2
medium  blr    del    1
        lon    del    9
        ny     del    1
dtype: int64


print (s.loc['medium'])
start  end
blr    del    1
lon    del    9
ny     del    1
dtype: int64


print (s.loc['low'])
start  end
lon    del    3
ny     del    2
dtype: int64

Answer 2

使用value_counts:

res = df[df['type'].eq('medium')].value_counts()
print(res)

输出

start  end  type  
lon    del  medium    9
ny     del  medium    1
blr    del  medium    1
dtype: int64

来自文档：

返回包含 DataFrame 中唯一行数的 Series。

如果您想从输出中删除类型，请按照@jezrael 的建议使用 droplevel：

res = df[df['type'].eq('medium')].value_counts().droplevel(level=-1)
print(res)

输出

start  end
lon    del    9
ny     del    1
blr    del    1
dtype: int64

这也可以扩展到所有类型，例如，使用：

res = df.value_counts(subset=['type', 'start', 'end']).sort_index(level=0)
print(res)

输出

type    start  end
low     lon    del    3
        ny     del    2
medium  blr    del    1
        lon    del    9
        ny     del    1
dtype: int64

Answer 3

df.where(lambda x:x.type == "medium").dropna().groupby(['start', 'end']).type.agg("count")

start  end
blr    del    1
lon    del    9
ny     del    1
Name: type, dtype: int64