pandas 熊猫在循环中合并数据帧
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pandas merging dataframes in a loop
提问by jake wong
I created a loop to read sqlite database into a pandas dataframe, and I am trying to merge them together based on "Code"
我创建了一个循环来将 sqlite 数据库读入一个 Pandas 数据帧，并且我试图基于 "Code"
...
df = pandas.Dataframe() # Creating an empty dataframe for merging at the end
items = ["tb1", "tb2", "tb3"]
for each_item in items:
my_value = pandas.read_sql_query('select "Code", "Name", "Value" from {tb_name} where "Value" is not null'
.format(tbl_name='"%s"' % each_item), con=engine)
print(my_value)
# This below code is my attempt to merge the dataframes that was obtained through the for loop
merge_value = pandas.merge(my_value, df, on='Code', how='outer')
my_value results:
my_value 结果：
# tb1 results
Code Name Value
0 C01 Name1 0.010000
1 C02 Name2 0.001200
2 C03 Name3 0.000300
3 C04 Name4 0.001700
# tb2 results
Code Name Value
0 C03 Name3 0.010000
1 C04 Name4 0.001200
2 C05 Name5 0.000300
3 C06 Name6 0.001700
# tb3 results
Code Name Value
0 C01 Name1 0.010000
1 C02 Name2 0.001200
2 C05 Name5 0.000300
3 C06 Name6 0.001700
I am trying to merge them into one table like below:
我正在尝试将它们合并到一张表中，如下所示：
# desired results
Code Name Value_x Value_y Value_Z
0 C01 Name1 0.010000 NULL 0.010000
1 C02 Name2 0.001200 NULL 0.001200
2 C03 Name3 0.000300 0.010000 NULL
3 C04 Name4 0.001700 0.001200 NULL
4 C05 Name5 NULL 0.000300 0.000300
5 C06 Name6 NULL 0.001700 0.001700
How do I merge it? I tried the below, but it produces key error: Code
我如何合并它？我试过下面的，但它产生key error: Code
merge_value = pandas.merge(my_value, df, on='Code', how='outer')
回答by Jeffrey Ram Pineda
You can use DataFrame.merge instead of pandas.merge
您可以使用 DataFrame.merge 而不是 pandas.merge
https://pandas.pydata.org/pandas-docs/stable/generated/pandas.DataFrame.merge.html
https://pandas.pydata.org/pandas-docs/stable/generated/pandas.DataFrame.merge.html
Create an empty DataFrame with the columns to prevent the "key error: Code"
使用列创建一个空的 DataFrame 以防止“关键错误：代码”
df = pd.DataFrame(columns=['Code'])
then in the loop, you
然后在循环中，你
df.merge(my_value, on='Code', how='outer')
after my_value is created
创建 my_value 后
