Question

我有一个多级列索引组对象，我试图从SQlite数据库发送和检索。 Pandas默认情况下将索引转换为一个看起来像元组的字符串（这很棒），但我遇到的问题是当读回表时，多级索引会丢失并且我留下字符串元组作为列标题。

以下是一个例子：

import pandas as pd
import numpy as np
import sqlite3

# Create a dataframe
data = {'Pets and Fruits'  : ["Apples", "Oranges", "Puppies", "Ducks"]*5,
        'C1'     : [1., 2., 3., 4.]*5,
        'C2'     : [1., 2., 3., 4.]*5,}
df = pd.DataFrame(data)

# Groupby dataframe
df = df.groupby("Pets and Fruits").agg(['sum', 'mean'])

# Create a sqlite database
db = sqlite3.connect("Fruits and Pets.sqlite")

# Send the group to the database
df.to_sql(name="fruits_and_pets", con=db, if_exists='replace')

# Read back the table
df_read = pd.read_sql_query('''SELECT * FROM fruits_and_pets''',con=db,index_col="Pets and Fruits")

print df
print df_read

在进入数据库之前：

                   C1         C2     
                  sum mean   sum mean
Pets and Fruits                      
Apples            5.0  1.0   5.0  1.0
Ducks            20.0  4.0  20.0  4.0
Oranges          10.0  2.0  10.0  2.0
Puppies          15.0  3.0  15.0  3.0

回到表格数据库：

                 ('C1', 'sum')  ('C1', 'mean')  ('C2', 'sum')  ('C2', 'mean')
Pets and Fruits                                                              
Apples                     5.0             1.0            5.0             1.0
Ducks                     20.0             4.0           20.0             4.0
Oranges                   10.0             2.0           10.0             2.0
Puppies                   15.0             3.0           15.0             3.0

我可以使用df_read.columns = pd.MultiIndex.from_tuples([eval(x) for x in df_read.columns])将数据帧转换回多级索引，但我想知道是否有更好的方法或内置的我缺少？

Answer 1

import pandas as pd
import numpy as np
import sqlite3

# Create a dataframe
data = {'Pets and Fruits'  : ["Apples", "Oranges", "Puppies", "Ducks"]*5,
        'C1'     : [1., 2., 3., 4.]*5,
        'C2'     : [1., 2., 3., 4.]*5,}
df = pd.DataFrame(data)

# Groupby dataframe
df = df.groupby("Pets and Fruits").agg(['sum', 'mean'])
df['Pets and Fruits'] = df.index.values
df = df.melt(id_vars='Pets and Fruits',var_name=['C','agg_type'])
# Create a sqlite database
db = sqlite3.connect("Fruits and Pets.sqlite")

# Send the group to the database
df.to_sql(name="fruits_and_pets", con=db, if_exists='replace',index=False)

# Read back the table
df_read = pd.read_sql_query('''SELECT * FROM fruits_and_pets''',con=db,index_col=["C","agg_type"])#,index_col=["Pets and Fruits",])
df_read = df_read.pivot(columns='Pets and Fruits').T
df_read.index = df_read.index.droplevel(0)
print(df)
print(df_read)

Pandas多级索引进出sql

1 个答案: