python - Pandas: print column name with missing values

Question

I am trying to print or to get list of columns name with missing values. E.g.

data1 data2 data3  
1     3     3  
2     NaN   5  
3     4     NaN  

I want to get ['data2', 'data3']. I wrote following code:

print('
'.join(map(
    lambda x : str(x[1])
    ,(filter(lambda z: z[0] != False, zip(train.isnull().any(axis=0), train.columns.values)))
)))

It works well, but I think should be simpler way.

Answer 1

df.isnull().any() generates a boolean array (True if the column has a missing value, False otherwise). You can use it to index into df.columns:

df.columns[df.isnull().any()]

will return a list of the columns which have missing values.

---

df = pd.DataFrame({'A': [1, 2, 3], 
                   'B': [1, 2, np.nan], 
                   'C': [4, 5, 6], 
                   'D': [np.nan, np.nan, np.nan]})

df
Out: 
   A    B  C   D
0  1  1.0  4 NaN
1  2  2.0  5 NaN
2  3  NaN  6 NaN

df.columns[df.isnull().any()]
Out: Index(['B', 'D'], dtype='object')

df.columns[df.isnull().any()].tolist()  # to get a list instead of an Index object
Out: ['B', 'D']