Pandas 根据其他列的累积逻辑运算创建条件列

Question

I have 2 columns that represent the on switch and off switch indicator. I want to create a column called last switch where it keeps record the 'last' direction of the switch (whether it is on or off). Another condition is that if both on and off switch value is 1 for a particular row, then the 'last switch' output will return the opposite sign of the previous last switch. Currently I managed to find a solution to get this almost correct except facing the situation where both on and off shows 1 that makes my code wrong.

I also attached the screenshot with a desired output. Please help appreciate all.

df=pd.DataFrame([[1,0],[1,0],[0,1],[0,1],[0,0],[0,0],[1,0],[1,1],[0,1],[1,0],[1,1],[1,1],[0,1]], columns=['on','off'])

df['last_switch']=(df['on']-df['off']).replace(0,method='ffill')

Answer 1

Add the following lines to your existing code:

for i in range(df.shape[0]):
    df['prev']=df['last_switch'].shift()
    df.loc[(df['on']==1) & (df['off']==1), 'last_switch']=df['prev'] * (-1)
df.drop('prev', axis=1, inplace=True)
df['last_switch']=df['last_switch'].astype(int)

Output:

    on  off  last_switch
0    1    0            1
1    1    0            1
2    0    1           -1
3    0    1           -1
4    0    0           -1
5    0    0           -1
6    1    0            1
7    1    1           -1
8    0    1           -1
9    1    0            1
10   1    1           -1
11   1    1            1
12   0    1           -1

Let me know if you need expanation of the code

Answer 2

df=pd.DataFrame([[1,0],[1,0],[0,1],[0,1],[0,0],[0,0],[1,0],[1,1],[0,1],[1,0],[1,1],[1,1],[0,1]], columns=['on','off'])
df['last_switch']=(df['on']-df['off']).replace(0,method='ffill')

prev_row = None
def apply_logic(row):
    global prev_row
    if prev_row is not None:
        if (row["on"] == 1) and (row["off"] == 1):
            row["last_switch"] = -prev_row["last_switch"]
    prev_row = row.copy()
    return row
df.apply(apply_logic,axis=1)

personally i am not a big fan of using loop against dataframe. shift wont work in this case as the "last_switch" column is dynamic and subject to change based on on&off status. Using your intermediate reesult with apply while carrying the value from previous row should do the trick. Hope it makes sense.