[英]How do you get two functions to return when using a user-defined function?
I am just starting to use user-defined functions, so this is probably not a very complex question, forgive me. 我刚刚开始使用用户定义的函数,所以请原谅这可能不是一个非常复杂的问题。
I have a few dataframes, which all have a column named 'interval_time' (for example) and I would like to rename this column 'Timestamp', and then make this renamed column into the index. 我有几个数据框,所有的数据框都有一个名为“ interval_time”的列(例如),我想将此列重命名为“ Timestamp”,然后将此重命名的列设置为索引。
I know that I can do this manually with this; 我知道我可以用这个手动完成;
df = df.rename(index=str, columns={'interval_time': 'Timestamp'})
df = df.set_index('Timestamp')
but now I would like to define a function called rename that does this for me. 但现在我想定义一个名为重命名的函数来为我完成此任务。 I have seen that this works;
我已经看到这行得通;
def rename_col(data, col_in='tempus_interval_time', col_out='Timestamp'):
return data.rename(index=str, columns={col_in: col_out}, inplace=True)
but when I try to add the second function it does not seem to do anything, but if I define the second part as its own function and run it it does seem to work. 但是,当我尝试添加第二个函数时,它似乎没有任何作用,但是,如果我将第二个部分定义为其自己的函数并运行它,则它似乎确实可以工作。
I am trying this 我正在尝试
def rename_n_index(data, col_in='tempus_interval_time', col_out='Timestamp'):
return data.rename(index=str, columns={col_in: col_out}, inplace=True)
return data.set_index('Timestamp', inplace=True)
The dataframes that I am using have the following form; 我正在使用的数据框具有以下形式;
df_scada
interval_time A ... X Y
0 2010-11-01 00:00:00 0.0 ... 396.36710 381.68860
1 2010-11-01 00:05:00 0.0 ... 392.97974 381.40634
2 2010-11-01 00:10:00 0.0 ... 390.15695 379.99493
3 2010-11-01 00:15:00 0.0 ... 389.02786 379.14810
You don't need to return anything , because your operations are done in place . 您不需要返回任何东西 ,因为您的操作已就位 。 You can do the in-place changes in your function:
您可以在函数中进行就地更改:
def rename_n_index(data, col_in='tempus_interval_time', col_out='Timestamp'):
data.rename(index=str, columns={col_in: col_out}, inplace=True)
data.set_index('Timestamp', inplace=True)
and any other references to the dataframe you pass into the function will see the changes made: 您传递给函数的数据框的任何其他引用都将看到所做的更改:
>>> import pandas as pd
>>> df = pd.DataFrame({'interval_time': pd.to_datetime(['2010-11-01 00:00:00', '2010-11-01 00:05:00', '2010-11-01 00:10:00', '2010-11-01 00:15:00']),
... 'A': [0.0] * 4}, index=range(4))
>>> df
A interval_time
0 0.0 2010-11-01 00:00:00
1 0.0 2010-11-01 00:05:00
2 0.0 2010-11-01 00:10:00
3 0.0 2010-11-01 00:15:00
>>> def rename_n_index(data, col_in='tempus_interval_time', col_out='Timestamp'):
... data.rename(index=str, columns={col_in: col_out}, inplace=True)
... data.set_index('Timestamp', inplace=True)
...
>>> rename_n_index(df, 'interval_time')
>>> df
A
Timestamp
2010-11-01 00:00:00 0.0
2010-11-01 00:05:00 0.0
2010-11-01 00:10:00 0.0
2010-11-01 00:15:00 0.0
In the above example, the df
reference to the dataframe shows the changes made by the function. 在上面的示例中,对数据帧的
df
引用显示了该函数所做的更改。
If you remove the inplace=True
arguments, the method calls return a new dataframe object. 如果删除
inplace=True
参数,则该方法调用将返回一个新的dataframe对象。 You can store an intermediate result as a local variable, then apply the second method to the dataframe referenced in that local variable: 您可以将中间结果存储为局部变量,然后将第二种方法应用于该局部变量中引用的数据框:
def rename_n_index(data, col_in='tempus_interval_time', col_out='Timestamp'):
renamed = data.rename(index=str, columns={col_in: col_out})
return renamed.set_index('Timestamp')
or you can chain the method calls directly to the returned object: 或者,您可以将方法调用直接链接到返回的对象:
def rename_n_index(data, col_in='tempus_interval_time', col_out='Timestamp'):
return data.rename(index=str, columns={col_in: col_out})\
.set_index('Timestamp'))
Because renamed
is already a new dataframe, you can apply the set_index()
call in-place to that object, then return just renamed
, as well: 因为
renamed
已经是一个新的数据帧,所以可以将set_index()
调用就地应用于该对象,然后也返回刚刚renamed
:
def rename_n_index(data, col_in='tempus_interval_time', col_out='Timestamp'):
renamed = data.rename(index=str, columns={col_in: col_out})
renamed.set_index('Timestamp', inplace=True)
return renamed
Either way, this returns a new dataframe object, leaving the original dataframe unchanged: 无论哪种方式,这都会返回一个新的数据框对象,而使原始数据框保持不变:
>>> def rename_n_index(data, col_in='tempus_interval_time', col_out='Timestamp'):
... renamed = data.rename(index=str, columns={col_in: col_out})
... return renamed.set_index('Timestamp')
...
>>> df = pd.DataFrame({'interval_time': pd.to_datetime(['2010-11-01 00:00:00', '2010-11-01 00:05:00', '2010-11-01 00:10:00', '2010-11-01 00:15:00']),
... 'A': [0.0] * 4}, index=range(4))
>>> rename_n_index(df, 'interval_time')
A
Timestamp
2010-11-01 00:00:00 0.0
2010-11-01 00:05:00 0.0
2010-11-01 00:10:00 0.0
2010-11-01 00:15:00 0.0
>>> df
A interval_time
0 0.0 2010-11-01 00:00:00
1 0.0 2010-11-01 00:05:00
2 0.0 2010-11-01 00:10:00
3 0.0 2010-11-01 00:15:00
See @MartijnPieters' explanation for resolving the errors in your code. 有关解决代码中的错误的信息,请参见@MartijnPieters的说明 。
However, note that the Pandorable method is to use method chaining. 但是,请注意Pandorable方法是使用方法链接。 Some find it aesthetically pleasing to see method names visually aligned.
有些人发现从外观上看方法名称在美学上令人愉悦。 Here's an example:
这是一个例子:
def rename_n_index(data, col_in='tempus_interval_time', col_out='Timestamp'):
renamed = data.rename(index=str, columns={col_in: col_out})\
.set_index('Timestamp')
return renamed
Then to apply these to a sequence of dataframes as in your previous question : 然后,将这些应用到dataframes序列在以前的问题 :
dfs = [df.pipe(rename_n_index) for df in (df1, df2, df3)]
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