How to get the value of the 2nd true above-CodePudding

expected result table

    A   cond    expect
0   0.12    FALSE   
1   0.38    TRUE    
2   0.93    FALSE   
3   0.42    FALSE   
4   0.18    TRUE    
5   0.86    FALSE   0.38
6   0.43    FALSE   0.38
7   0.99    TRUE    
8   0.84    FALSE   0.18
9   0.65    FALSE   0.18

I want to get the value of ‘A’ column when the ‘cond’ column is true

But what I want is the value of the 2nd true above

CodePudding user response：

We can do where with your cond , then get the value for all True after dropna then we shift the value and reindex back with ffill

df.loc[~df['cond'],'expect'] = df['A'].where(df['cond']).dropna().shift().reindex(df.index).ffill()
df
Out[183]: 
      A   cond  expect
0  0.12  False     NaN
1  0.38   True     NaN
2  0.93  False     NaN
3  0.42  False     NaN
4  0.18   True     NaN
5  0.86  False    0.38
6  0.43  False    0.38
7  0.99   True     NaN
8  0.84  False    0.18
9  0.65  False    0.18

CodePudding user response：

If you want to ALWAYS obtain the value of the 2nd TRUE:

count = 1
val2 = 0
# Iterate over panda Data Frame
for index, row in df.iterrows():
    if row['cond'] == 'TRUE':
        # Get the Second TRUE value
        if count == 2:
            val2 = row['A']
            break
        count  = 1