Python – Drop row if two columns are NaN

Question

This is an extension to this question, where OP wanted to know how to drop rows where the values in a single column are NaN.

I’m wondering how I can drop rows where the values in 2 (or more) columns are both NaN. Using the second answer’s created Data Frame:

In [1]: df = pd.DataFrame(np.random.randn(10,3))

In [2]: df.ix[::2,0] = np.nan; df.ix[::4,1] = np.nan; df.ix[::3,2] = np.nan;

In [3]: df
Out[3]:
          0         1         2
0       NaN       NaN       NaN
1  2.677677 -1.466923 -0.750366
2       NaN  0.798002 -0.906038
3  0.672201  0.964789       NaN
4       NaN       NaN  0.050742
5 -1.250970  0.030561 -2.678622
6       NaN  1.036043       NaN
7  0.049896 -0.308003  0.823295
8       NaN       NaN  0.637482
9 -0.310130  0.078891       NaN

If I use the drop.na() command, specifically the drop.na(subset=[1,2]), then it completes an “or” type drop and leaves:

In[4]: df.dropna(subset=[1,2])
Out[4]: 
          0         1         2
1  2.677677 -1.466923 -0.750366
2       NaN  0.798002 -0.906038
5 -1.250970  0.030561 -2.678622
7  0.049896 -0.308003  0.823295

What I want is an “and” type drop, where it drops rows where there is an NaN in column index 1 and 2. This would leave:

          0         1         2
1  2.677677 -1.466923 -0.750366
2       NaN  0.798002 -0.906038
3  0.672201  0.964789       NaN
4       NaN       NaN  0.050742
5 -1.250970  0.030561 -2.678622
6       NaN  1.036043       NaN
7  0.049896 -0.308003  0.823295
8       NaN       NaN  0.637482
9 -0.310130  0.078891       NaN

where only the first row is dropped.

Any ideas?

EDIT: changed data frame values for consistency

Asked By: Kevin M

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Source

Answer 1

Any one of the following two:

df.dropna(subset=[1, 2], how='all')

or

df.dropna(subset=[1, 2], thresh=1)

Answered By: Alicia Garcia-Raboso

Answer 2

Specify dropna() method:

df.dropna(subset=[1,2], how='all')

Answered By: ragesz

Answer 3

The accepted answer didn’t work for me. I tried the following code and nothing changed in my dataframe.

df.dropna(subset=['col1', 'col2', 'col3', 'col4', 'col5', 'col6'], how='all', inplace=True)

EDIT: I think it didn’t work because ‘all’ refers to all columns in the df, and not all columns in the subset.
The thresh is also a bit confusing for me, because it’s a condition to keep rows, even though this a dropping function. In the OP, if I understand correctly, it’s required to have at least one non nan value to keep a row, and if a row has more than 2 nan values, it should be dropped.
In my case, I want to drop a row if all values in the columns of the subset have nan values, so I want to keep a row if all 6 values are not nan, and I don’t know if this corresponds to thresh=6.

These two commands also didn’t work for me:

df.dropna(subset=['col1', 'col2', 'col3', 'col4', 'col5', 'col6'], thres=6, inplace=True)
df.dropna(subset=['col1', 'col2', 'col3', 'col4', 'col5', 'col6'], how='all', thres=6, inplace=True)

and when I added axis=1 or axis='columns' in the parameters, I got a KeyError that the list of columns I am passing are not in the dataframe, and I don’t know the reason why.

I ended up iterating over the df like this, also because I realized that some supposedly NaN values, might not be caught, because they are Null or empty:

indices_to_drop = list()
for index, row in df.iterrows():
        if (pd.isnull(row["col1"]) or pd.isna(row["col1"]) or row["col1"] == "") and 
                (pd.isnull(row["col2"]) or pd.isna(row["col2"]) or row["col2"] == "") and 
                (pd.isnull(row["col3"]) or pd.isna(row["col3"]) or row["col3"]
                 == "") and 
                (pd.isnull(row["col4"]) or pd.isna(row["col4"]) or row["col4"] ==
                 "") 
                and 
                (pd.isnull(row["col5"]) or pd.isna(row["col5"]) or row[
                    "col6"] == "") and 
                (pd.isnull(row["col6"]) or pd.isna(row["col6"]) or row["col6"] == ""):
            indices_to_drop.append(index)
df.drop(labels=indices_to_drop, inplace=True)

Answered By: KLaz

Answer 4

I faced a similar issue where I’d 45 features(columns) and wanted to drop rows for only selected features having NaN values eg columns 7 to 45.

Step 1: I created a list (col_lst) from columns which I wanted to be operated for NaN

Step 2: df.dropna(axis = 0, subset = col_lst, how = 'all', inplace = True)

The above step removed only those rows fromthe dataframe which had all (not any) the columns from 7 to 45 with NaN values.

Answered By: Devendra Bharadwaj

Answer 5

Try this code below, I hope it can solve your problem

drop_rows = df.dropna( how='any',
                          subset=['Columns1', 'Columns2'])

Answered By: Rugaya Bsa

Python – Drop row if two columns are NaN

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