pandas fillna sequentially step by step-CodePudding

I have dataframe like as below

Re_MC,Fi_MC,Fin_id,Res_id,     
1,2,3,4
,7,6,11
11,,31,32
,,35,38

df1 = pd.read_clipboard(sep=',')

I would like to fillna based on two steps

a) First, compare only Re_MC and Fi_MC. If a value is missing in either of these columns, copy it from the other column.

b) Despite doing step a, if there is still NA for either Re_MC or Fi_MC, copy values from Fin_id for Fi_MC and Res_id for Re_MC.

So, I tried the below two approaches

Approach 1 - This works but not efficient/elegant

df1['Re_MC'] = df1['Re_MC'].fillna(df1['Fi_MC'])
df1['Fi_MC'] = df1['Fi_MC'].fillna(df1['Re_MC'])
df1['Re_MC'] = df1['Re_MC'].fillna(df1['Res_id'])
df1['Fi_MC'] = df1['Fi_MC'].fillna(df1['Fin_id'])

Approach 2 - This doesn't work and provide incorrect output

df1['Re_MC'] = df1['Re_MC'].fillna(df1['Fi_MC']).fillna(df1['Res_id'])
df1['Fi_MC'] = df1['Fi_MC'].fillna(df1['Re_MC']).fillna(df1['Fin_id'])

Is there any other efficient way to fillna in a sequential manner? Meaning, we do step a first and then based on result of step a, we do step b

I expect my output to be like as shown below

CodePudding user response：

You can use dictionaries in fillna:

(df1
 .fillna({'Re_MC': df1['Fi_MC'], 'Fi_MC': df1['Re_MC']})
 .fillna({'Re_MC': df1['Res_id'], 'Fi_MC': df1['Fin_id']})
)

output:

   Re_MC  Fi_MC  Fin_id  Res_id
0    1.0    2.0       3       4
1    7.0    7.0       6      11
2   11.0   11.0      31      32
3   38.0   35.0      35      38