将用户定义的函数应用于数据帧

Question

我试图编写的函数将获取提供的数据帧，计算F统计值，并将其作为输出

数据格式Final

Key      Color   Strength   Fabric  Sales
a         0         1         1       10
b         1         2         2       15

在这里，颜色、强度和织物是独立的，而销售是独立的

其思想是创建一个循环，为每个唯一的键值创建一个新的数据帧： 并在此数据帧上执行一个函数，然后创建一个新的数据帧，该数据帧是从唯一键值获得的所有新数据帧的集合

def regression():
    X=Final1.copy()
    y=Final1[['Sales']].copy()
    X_train, X_test, y_train, y_test = train_test_split(X,y,test_size=.2, random_state=0)
    sel=f_classif(X_train, y_train)
    p_values=pd.Series(sel[0], index=X_train.columns)
    p_values=p_values.reset_index()
    pd.options.display.float_format = "{:,.2f}".format
    return p_values

Finals=[]
Finals=pd.DataFrame(Finals)
for group in Final.groupby('Key'): 
    # group is a tuple where the first value is the Key and the second is the dataframe
    Final1=group[1]
    Final1=pd.DataFrame(Final1)
    result=regression()
    Finals=pd.concat([Finals, result], axis=1)


# do xyz with result

print(Finals)

这是我想出的代码，但它抛出了一个错误

---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-131-c3a3b53971d5> in <module>
      5     Final1=group[1]
      6     Final1=pd.DataFrame(Final1)
----> 7     result=regression()
      8     Finals=pd.concat([Finals, result], axis=1)
      9 

<ipython-input-120-d5c718baaba8> in regression()
      2     X=Final1.iloc[:,7:-1].copy()
      3     y=Final1[['Sale Rate']].copy()
----> 4     X_train, X_test, y_train, y_test = train_test_split(X,y,test_size=.2, random_state=0)
      5     sel=f_classif(X_train, y_train)
      6     p_values=pd.Series(sel[0], index=X_train.columns)

~\anaconda3\lib\site-packages\sklearn\model_selection\_split.py in train_test_split(*arrays, **options)
   2120     n_samples = _num_samples(arrays[0])
   2121     n_train, n_test = _validate_shuffle_split(n_samples, test_size, train_size,
-> 2122                                               default_test_size=0.25)
   2123 
   2124     if shuffle is False:

~\anaconda3\lib\site-packages\sklearn\model_selection\_split.py in _validate_shuffle_split(n_samples, test_size, train_size, default_test_size)
   1803             'resulting train set will be empty. Adjust any of the '
   1804             'aforementioned parameters.'.format(n_samples, test_size,
-> 1805                                                 train_size)
   1806         )
   1807 

ValueError: With n_samples=1, test_size=0.2 and train_size=None, the resulting train set will be empty. Adjust any of the aforementioned parameters.

这个代码可能出了什么问题

Answer 1

一个简单的解决方案是：

for group in Final.groupby('Key'): 
    # group is a tuple where the first value is the Key and the second is the dataframe
    result = regression(group[1])
    # do xyz with result

编辑：

您不必再次将组转换为数据帧，并且可以直接使用它，因为它已经采用了正确的格式

# this line is not necessary
Final1 = pd.DataFrame(Final1)

从错误判断，很明显，您传递到train_test_split函数的group没有足够的记录。这在错误消息中非常明显。您必须使用try来处理此类错误，除非

Answer 2

只要我过滤掉所有少于10个观察值的键，代码就会工作