條件函數

Question

我有一個csv文件像這樣：

  Landform    Number   Name Class 
0  Deltaic Plain   912   Lx  NaN 
1 Hummock and Swale   912   Lx  NaN 
2   Sand Dunes   912   Lx  NaN 
3 Hummock and Swale   939  Woodbury NaN 
4   Sand Dunes   939  Woodbury NaN 

當地貌包含Deltaic Plain，特定NameHummock and Swale和Sand Dunes我要值1分配給Class。

當Landform包含Hummock and Swale和Sand Dunes我想爲Class分配值2。

我所需的輸出是：

  Landform    Number   Name Class 
0  Deltaic Plain   912   Lx  1 
1 Hummock and Swale   912   Lx  1 
2   Sand Dunes   912   Lx  1 
3 Hummock and Swale   939  Woodbury 2 
4   Sand Dunes   939  Woodbury 2 

我知道如何爲剛1行這樣做：

def f(x): 
    if x['Landform'] == 'Hummock and Swale' : return '1' 
    else: return '2' 

df['Class'] = df.apply(f, axis=1) 

，但我不知道如何通過Name組，然後創建基於多行的條件函數。

Answer 1

這個想法是在您的Number列上進行分組，並應用一個查看該組中所有地形並返回適當類的函數。這裏有一個例子：

def determineClass(landforms): 
    if all(form in landforms.values for form in ('Deltaic Plain', 'Hummock and Swale', 'Sand Dunes')): 
     return 1 
    elif all(form in landforms.values for form in ('Hummock and Swale', 'Sand Dunes')): 
     return 2 
    # etc. 
    else: 
     # return "default" class 
     return 0 

>>> df.groupby('Number').Landform.apply(determineClass) 
Number 
912 1 
939 2 
Name: Landform, dtype: int64 

如果你想分配值回班列，只需使用map，從20分鐘前在this question描述：

>>> classes = df.groupby('Number').Landform.apply(determineClass) 
>>> df['Class'] = df.Number.map(classes) 
>>> df 
      Landform Number  Name Class 
0  Deltaic Plain  912  Lx  1 
1 Hummock and Swale  912  Lx  1 
2   Sand Dunes  912  Lx  1 
3 Hummock and Swale  939 Woodbury  2 
4   Sand Dunes  939 Woodbury  2