Fill NaN values in dataframe with pandas

Question

I have a dataframe that I created from a text file. Columns BF should apply to all null fields below them, then once all nulls are filled the next set of periods should be filled by the next values populated in BF. How would I go about accomplishing this?

Answer 1

You'll want to use the fillna() method of DataFrames, with a forward-fill:

df.fillna(method='ffill')

Here's a quick example:

df = pd.DataFrame({'A': [4, None, None, 5, None, None],
                   'B': [2, None, None, 3, None, None],
                   'C': range(6)})

>>> df
    A   B  C
0   4   2  0
1 NaN NaN  1
2 NaN NaN  2
3   5   3  3
4 NaN NaN  4
5 NaN NaN  5

>>> df.fillna(method='ffill')
   A  B  C
0  4  2  0
1  4  2  1
2  4  2  2
3  5  3  3
4  5  3  4
5  5  3  5