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

Here's a tidy way to do it using Pandas: Swap all the NaN for empty strings, and return whatever string value is in each row. If a row is empty, return what came before it.

import pandas as pd

def decide(data):
    if len(data.sum()):
        return data.sum()
    return decide(df.iloc[data.name - 1])

df.fillna("", inplace=True)
df.apply(decide, axis=1)

Output:

index
0      Buy
1      Buy
2     Sell
3     Sell
4      Buy
5     Sell
6     Sell
7     Sell
8     Sell
9      Buy
10    Sell
dtype: object

Note: Making a couple of assumptions here. First, assuming only Buy or Sell occurs in a row. Second, assuming first row is not empty.

Data:

df = pd.read_clipboard(index_col="index") # copied from OP