Python：根据熊猫数据框中的两列（变量）获取频率计数

Question

您好，我有以下数据框。

Group   Size 

    Short   Small 
    Short   Small 
    Moderate  Medium 
    Moderate  Small 
    Tall   Large 

我想统计同一行出现在数据帧中的次数。

Group   Size  Time 

    Short   Small  2 
    Moderate  Medium  1 
    Moderate  Small  1 
    Tall   Large  1 

Answer 1

您可以使用GROUPBY的size：

In [11]: df.groupby(["Group", "Size"]).size() 
Out[11]: 
Group  Size 
Moderate Medium 1 
      Small  1 
Short  Small  2 
Tall  Large  1 
dtype: int64 

In [12]: df.groupby(["Group", "Size"]).size().reset_index(name="Time") 
Out[12]: 
     Group Size Time 
0 Moderate Medium  1 
1 Moderate Small  1 
2  Short Small  2 
3  Tall Large  1 

Answer 2

您也可以尝试pd.crosstab()

Group   Size 

Short   Small 
Short   Small 
Moderate  Medium 
Moderate  Small 
Tall   Large 

pd.crosstab(df.Group,df.Size) 


Size  Large Medium Small 
Group       
Moderate  0  1  1 
Short   0  0  2 
Tall   1  0  0 

编辑：为了让你出把

pd.crosstab(df.Group,df.Size).replace(0,np.nan).\ 
    stack().reset_index().rename(columns={0:'Time'}) 
Out[591]: 
     Group Size Time 
0 Moderate Medium 1.0 
1 Moderate Small 1.0 
2  Short Small 2.0 
3  Tall Large 1.0