How to add a missing index observation in a multi Index

Question

I frequently get new datasets with new variables from time to and want to make them symmetrical for comparison purposes.

Data is multiple indexed, where each profile can have an impact from [-2,+2] with values varying over the years.

A) CAN'T --> Don't understand how to add missing profile index 'RPG'

B) CAN --> I am able to add all the values from [-2,2].

Therefore, I just need to add 1 line with the index 'RPG' (even better if it could be symmetrical from the start, but it's not a problem)

import numpy as np
import pandas as pd

list_profile = ['gun','bat','RPG']

df = pd.DataFrame({'profile': ['gun','gun','gun','bat','bat','bat'],
                    'impact': [-1, 0, 1, -1, 0, 1],
                    '2020':   [-10, 0, 15, -3, 0, 4],
                    '2021':   [-20, 0, 30, -6, 0, 8],})
print(df)

#---------------------------------------------------------------------
# A)  UNELEGANT SOLUTION I WAS THINKING ABOUT THAT DOESN'T WORK : 
#---------------------------------------------------------------------
df = df.set_index('profile')
for profile in list_profile
    try:
      df.loc[profile]
    except ValueError:
        # ADD OBSERVATION FOR MISSING INDEX RPG
#---------------------------------------------------------------------

# B)  Code for expanding 'impact' from [-1,1] to [-2,2] :
#----------------------------------------------------------
mux = pd.MultiIndex.from_product([df['profile'].unique(),
                                  np.arange(-2,2+1)],
                                 names=['profile','impact'])

df = df.set_index(['profile', 'impact']).reindex(mux).reset_index()
df = df.fillna(0)
df
``

Answer 1

IIUC, do you want?

mux = pd.MultiIndex.from_product([list_profile, np.arange(-2,2+1)], names=['profile', 'impact'])

df.set_index(['profile', 'impact']).reindex(mux, fill_value=0).reset_index()

Output:

   profile  impact  2020  2021
0      gun      -2     0     0
1      gun      -1   -10   -20
2      gun       0     0     0
3      gun       1    15    30
4      gun       2     0     0
5      bat      -2     0     0
6      bat      -1    -3    -6
7      bat       0     0     0
8      bat       1     4     8
9      bat       2     0     0
10     RPG      -2     0     0
11     RPG      -1     0     0
12     RPG       0     0     0
13     RPG       1     0     0
14     RPG       2     0     0