data cleaning - Fill missing Values by a ratio of other values in Pandas

Question

I have a column in a Dataframe in Pandas with around 78% missing values.

The remaining 22% values are divided between three labels - SC, ST, GEN with the following ratios.

SC - 16% ST - 8% GEN - 76%

I need to replace the missing values by the above three values so that the ratio of all the elements remains same as above. The assignment can be random as long the the ratio remains as above.

How do I accomplish this?

Answer 1

Starting with this DataFrame (only to create something similar to yours):

import numpy as np
df = pd.DataFrame({'C1': np.random.choice(['SC', 'ST', 'GEN'], p=[0.16, 0.08, 0.76], 
                                          size=1000)})
df.loc[df.sample(frac=0.22).index] = np.nan

It yields a column with 22% NaN and the remaining proportions are similar to yours:

df['C1'].value_counts(normalize=True, dropna=False)
Out: 
GEN    0.583
NaN    0.220
SC     0.132
ST     0.065
Name: C1, dtype: float64

df['C1'].value_counts(normalize=True)
Out: 
GEN    0.747436
SC     0.169231
ST     0.083333
Name: C1, dtype: float64

Now you can use fillna with np.random.choice:

df['C1'] = df['C1'].fillna(pd.Series(np.random.choice(['SC', 'ST', 'GEN'], 
                                                      p=[0.16, 0.08, 0.76], size=len(df))))

The resulting column will have these proportions:

df['C1'].value_counts(normalize=True, dropna=False)
Out: 
GEN    0.748
SC     0.165
ST     0.087
Name: C1, dtype: float64