Drop nan rows unless string value in separate column - Pandas

Question

I want to drop rows containing NaN values except if a separate column contains a specific string. Using the df below, I want to drop rows if NaN in Code2, Code3 unless the string A is in Code1.

df = pd.DataFrame({   
        'Code1' : ['A','A','B','B','C','C'],    
        'Code2' : ['B',np.nan,'A','B',np.nan,'B'],    
        'Code3' : ['C',np.nan,'C','C',np.nan,'A'],                                   
        })

def dropna(df, col):

    if col == np.nan:
        df = df.dropna()

    return df

df = dropna(df, df['Code2'])

Intended Output:

  Code1 Code2 Code3
0     A     B     C
1     A   NaN   NaN
2     B     A     C
3     B     B     C
4     C     B     A

ansev · Accepted Answer · 2019-11-14 00:05:56Z

3

Use DataFrame.notna + DataFrame.all to performance a boolean indexing:

new_df=df[df.Code1.eq('A')|df.notna().all(axis=1)]
print(new_df)

  Code1 Code2 Code3
0     A     B     C
1     A   NaN   NaN
2     B     A     C
3     B     B     C
5     C     B     A

answered Nov 14, 2019 at 0:05

ansev

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