Python: How to join back df after groupby appropriately

Question

I have a df:

df = pd.DataFrame({'CaseNo':[1,1,1,1,2,2,2,2],
                    'Movement_Sequence_No':[1,2,3,4,1,2,3,4],
                    'Movement_Start_Date':['2020-02-09 22:17:00','2020-02-10 17:19:41','2020-02-17 08:04:19',
                                           '2020-02-18 11:22:52','2020-02-12 23:00:00','2020-02-24 10:26:35',
                                           '2020-03-03 17:50:00','2020-03-17 08:24:19'],
                    'Movement_End_Date':['2020-02-10 17:19:41','2020-02-17 08:04:19','2020-02-18 11:22:52',
                                         '2020-02-25 13:55:37','2020-02-24 10:26:35','2020-03-03 17:50:00',
                                         '2222-12-31 23:00:00','2020-03-18 18:50:00'],
                    'Category':['A','A','ICU','A','B','B','B','B'],
                    'RequestDate':['2020-02-10 16:00:00','2020-02-16 13:04:20','2020-02-18 07:11:11','2020-02-21 21:30:30',
                                   '2020-02-13 22:00:00','NA','2020-03-15 09:40:00','2020-03-18 15:10:10'],
                    'Test1':['180','189','190','188','328','NA','266','256'],
                    'Test2':['20','21','15','10','33','30','28','15'],
                    'Test3':['55','NA','65','70','58','64','68','58'],
                    'Age':['65','65','65','65','45','45','45','45']})

After doing some processing to fill missing values, I get df2:

# Format df appropriately
df = df.replace('NA', np.nan)
df[['Test1','Test2','Test3','Age']] = df[['Test1','Test2','Test3','Age']].astype(float)

# helper column to segregate non-ICU cols by value 0
df["helper"] = df.groupby("CaseNo")["Category"].transform(lambda d: d.eq("ICU").cumsum())

df2 = df.loc[df["helper"].eq(0)].groupby("CaseNo", as_index=False).fillna(
    method='ffill').reset_index().drop('index', axis=1)  # ffill will fill NA w the latest/prev test value

How do I merge df2 back appropriately into df so that the changes will be updated in df? Expected outcome:

Answer 1

From what I understand , you can try with df.where after setting up 2 conditions

out = df.replace('NA',np.nan)
cond = out['Category'].ne('ICU') & out['RequestDate'].isna()
out = out.groupby('CaseNo',as_index=False).fillna(method='ffill').where(cond,df)


#if you want Test3 in row 2 to be NaN and not 'NA'
#out = out.groupby('CaseNo',as_index=False).fillna(method='ffill').where(cond,out)

display(out)

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