Creating an IF statement in Python that looks at previous IF statement output

Question

I am having difficulty creating an IF statement that does the following:

• If C1 = Buy, then Buy
• If C2 = Sell, then Sell
• If C1 & C2 = nan,

Answer 1

You can use pd.DataFrame.ffill along axis=1 followed by pd.Series.ffill:

df['C3'] = df[['C1', 'C2']].ffill(axis=1).iloc[:, -1].ffill()

print(df)

    index   C1    C2    C3
0       0  Buy   NaN   Buy
1       1  NaN   NaN   Buy
2       2  NaN  Sell  Sell
3       3  NaN   NaN  Sell
4       4  Buy   NaN   Buy
5       5  NaN  Sell  Sell
6       6  NaN  Sell  Sell
7       7  NaN   NaN  Sell
8       8  NaN   NaN  Sell
9       9  Buy   NaN   Buy
10     10  NaN  Sell  Sell