将行值重复 X 次

Question

I have a dataframe with the following data:

        Stock:      Bond:      Gold:  
2/01/19 NaN         NaN        NaN
1/31/19 NaN         NaN        NaN
1/30/19 33%         33%        33%
1/29/19 NaN         NaN        NaN
1/28/19 NaN         NaN        NaN
1/27/19 50%         20%        30%
1/26/19 NaN         NaN        NaN
1/25/19 NaN         NaN        NaN
1/24/19 NaN         NaN        NaN
1/23/19 NaN         NaN        NaN
1/22/29 40%         50%        10%

I want all the NaN to be replaced with the % value that's beneath it, so that the final output would like the below:

        Stock:      Bond:      Gold:  
2/01/19 33%         33%        33%
1/31/19 33%         33%        33%
1/30/19 33%         33%        33%
1/29/19 50%         20%        30%
1/28/19 50%         20%        30%
1/27/19 50%         20%        30%
1/26/19 40%         50%        10%
1/25/19 40%         50%        10%
1/24/19 40%         50%        10%
1/23/19 40%         50%        10%
1/22/29 40%         50%        10%

Is there a way to achieve this without using loops?

Answer 1

Use back filling missing values by bfill , what is short version of DataFrame.fillna with method='bfill' :

df = df.bfill()
#alternative
#df = df.fillna(method='bfill')
print (df)
        Stock: Bond: Gold:
2/01/19    33%   33%   33%
1/31/19    33%   33%   33%
1/30/19    33%   33%   33%
1/29/19    50%   20%   30%
1/28/19    50%   20%   30%
1/27/19    50%   20%   30%
1/26/19    40%   50%   10%
1/25/19    40%   50%   10%
1/24/19    40%   50%   10%
1/23/19    40%   50%   10%
1/22/29    40%   50%   10%