python - 数据帧字典中列的总和

Question

我如何使用数据框字典？或者，是否有更好的方法来概览我的数据？例如，如果我有:

Fruit   Qty Year
Apple   2   2016
Orange  1   2017
Mango   2   2016
Apple   9   2016
Orange  8   2015
Mango   7   2016
Apple   6   2016
Orange  5   2017
Mango   4   2015

然后我试图找出我每年总共得到多少，例如:

        2015    2016    2017
Apple   0       11      0
Orange  8       0       6
Mango   4       9       0

我写了一些代码，但可能没有用:

import pandas as pd

# Fruit Data
df_1 = pd.DataFrame({'Fruit':['Apple','Orange','Mango','Apple','Orange','Mango','Apple','Orange','Mango'], 'Qty': [2,1,2,9,8,7,6,5,4], 'Year': [2016,2017,2016,2016,2015,2016,2016,2017,2015]})

# Create a list of Fruits
Fruits = df_1.Fruit.unique()

# Break down the dataframe by Year
df_2015 = df_1[df_1['Year'] == 2015]
df_2016 = df_1[df_1['Year'] == 2016]
df_2017 = df_1[df_1['Year'] == 2017]

# Create a dataframe dictionary of Fruits
Dict_2015 = {elem : pd.DataFrame for elem in Fruits}
Dict_2016 = {elem : pd.DataFrame for elem in Fruits}
Dict_2017 = {elem : pd.DataFrame for elem in Fruits}

# Store the Qty for each Fruit x each Year
for Fruit in Dict_2015.keys():
    Dict_2015[Fruit] = df_2015[:][df_2015.Fruit == Fruit]
for Fruit in Dict_2016.keys():
    Dict_2016[Fruit] = df_2016[:][df_2016.Fruit == Fruit]
for Fruit in Dict_2017.keys():
    Dict_2017[Fruit] = df_2017[:][df_2017.Fruit == Fruit]

Answer 1

您可以使用pandas.pivot_table .

res = df.pivot_table(index='Fruit', columns=['Year'], values='Qty',
                     aggfunc=np.sum, fill_value=0)

print(res)

Year    2015  2016  2017
Fruit                   
Apple      0    17     0
Mango      4     9     0
Orange     8     0     6

有关使用指南，请参阅 How to pivot a dataframe .