如果行中不包含模式，请使用groupby删除GroupB

Question

你好，我有一个数据帧，比如

col1 col2
G1 OP2
G1 OP0
G1 OPP
G1 OPL_Lh
G2 OII
G2 OIP
G2 IOP
G3 TYU
G4 TUI
G4 TYUI
G4 TR_Lh

我想通过groupby并从df-tha组中删除，这些组在col2中不包含至少一行包含

'_Lh' 

在这里，我应该只保留G1和G4并获得：

col1 col2
G1 OP2
G1 OP0
G1 OPP
G1 OPL_Lh
G4 TUI
G4 TYUI
G4 TR_Lh

有人有主意吗？多谢各位

Answer 1

解决这个问题还有很长的路要走，来说明groupby是如何工作的

首先创建一个函数，用于测试所需字符串：

def contains_str(x, string = '_Lh'):
    if string in x:
        return True
    else:
        return False

接下来，迭代您的组并应用此函数：

keep_dict = {}

for label, group_df in df.groupby('col1'):
    keep = group_df['col2'].apply(contains_str).any()
    keep_dict[label] = keep

print(keep_dict)
# {'G1': True, 'G2': False, 'G3': False, 'G4': True}

Feel free to print individual items in the operation to understand their role.

最后，将该词典映射到您当前的df:

df_final = df[df['col1'].map(keep_dict)].reset_index(drop=True)

    col1    col2
0   G1      OP2
1   G1      OP0
2   G1      OPP
3   G1      OPL_Lh
4   G4      TUI
5   G4      TYUI
6   G4      TR_Lh

---

您可以使用以下代码压缩这些步骤：

keep_dict = df.groupby('col1', as_index=True)['col2'].apply(lambda arr: any([contains_str(x) for x in arr])).to_dict()

print(keep_dict)
# {'G1': True, 'G2': False, 'G3': False, 'G4': True}

I hope this both answers your Q and explains what's taking place "behind the scenes" in groupby operations.