Pandas Dataframe: substract and divided two rows value based on column condition

Question

I have DataFrame:

A	B	C	D
1	0.1	0.2	0.3
2	0.4	0.7	0.2
3	0	4.25	100
3	-2.5	4.20	70
3	-2.5	3.5	80
4	0	3.6	81
4	-5	3.5	77
4	-5	3.4	75
4	-5	3.1	74
5	0	3.2	75
5	0.1	3.3	73

Now , i want to skip first two rows. after that i want to substarct last row value and first row value for number ‘3’ with coumn ‘C’ value then divide with same substactction but with coumn ‘B’ Value. basically, |3.5-4.25|/|-2.5-0| = | 0.3 |

i tried and skiped first two rows with

cols = ['A']
df[cols] = df[df[cols] > 2][cols]
df = df.dropna()

Expected output:

NEW_COL	Result
1	0.3
2	0.1
3	1

could you please help me?

Asked By: stefan

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Source

Answer 1

IIUC, you can compute the last-first per group, then divide C/B and drop NAs:

out = (df.groupby('A')
         .agg(lambda g: abs(g.iloc[-1]-g.iloc[0]))
         .eval('C/B')
         .dropna()
         .reset_index(drop=True)
      )

output:

0    0.3
1    0.1
2    1.0
dtype: float64

Answered By: mozway

Pandas Dataframe: substract and divided two rows value based on column condition

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