Issue
I am trying to add values to a column using a formula, using the information from this question: Is there a way in Pandas to use previous row value in dataframe.apply when previous value is also calculated in the apply?
I already have the first number of the column B and I want to make a formula for the rest of column B.
The dataframe looks something like this:
A B C
0.16 0.001433 25.775485
0.28 0 25.784443
0.28 0 25.792396
...
And the method I tried was:
for i in range(1, len(df)):
df.loc[i, "B"] = df.loc[i-1, "B"] + df.loc[i,"A"]*((df.loc[i,"C"]) - (df.loc[i-1,"C"]))
But this code produces an infinite loop, can someone help me with this?
Solution
you can use shift
and a simple assignment.
The general rule in pandas if you use loops
you're doing something wrong, it's considered an anti pattern.
df['B_new'] = df['B'].shift(-1) - df['A'] * ((df['C'] - df['C'].shift(-1)))
A B C B_new
0 0.16 0.001433 25.775485 0.001433
1 0.28 0.000000 25.784443 0.002227
2 0.28 0.000000 25.792396 NaN
Answered By - Umar.H
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