python 3.x - Repeat the value in column until a change occurs

Question

I have the following df:

df = pd.DataFrame(data = {'Location': ['ALABAMA', 'Auburn', 'Florence', 'Jacksonville', 'ALASKA', 'Fairbanks'], 'State': ['ALABAMA', np.nan, np.nan, np.nan, 'ALASKA', np.nan]})

       Location    State
0       ALABAMA  ALABAMA
1        Auburn      NaN
2      Florence      NaN
3  Jacksonville      NaN
4        ALASKA   ALASKA
5     Fairbanks      NaN

What I want is to replace the NaN values in the 'State' column with their corresponding state name. In other words, repeat the value in column until a change occurs. This is the desired output:

df_output = pd.DataFrame(data = {'Location': ['ALABAMA', 'Auburn', 'Florence', 'Jacksonville', 'ALASKA', 'Fairbanks'], 'State': ['ALABAMA', 'ALABAMA', 'ALABAMA', 'ALABAMA', 'ALASKA', 'ALASKA']})

       Location    State
0       ALABAMA  ALABAMA
1        Auburn  ALABAMA
2      Florence  ALABAMA
3  Jacksonville  ALABAMA
4        ALASKA   ALASKA
5     Fairbanks   ALASKA

Any idea?

Answer 1

If your top dataframe image is what you have already then this is a simple problem.

df['State'].fillna(method='ffill')