Pandas reverse of diff()

Question

I have calculated the differences between consecutive values in a series, but I cannot reverse / undifference them using diffinv():

ds_sqrt = np.sqrt(ds)
ds_sqrt = pd.DataFrame(ds_sqrt)
ds_diff = ds_sqrt.diff().values

How can I undifference this?

Answer 1

Reverse diff in one line with pandas

import pandas as pd

df = pd.DataFrame([10, 15, 14, 18], columns = ['Age'])
df['Age_diff'] = df.Age.diff()

df['reverse_diff'] = df['Age'].shift(1) + df['Age_diff']

print(df)

    Age  Age_diff  reverse_diff
0   10       NaN           NaN
1   15       5.0          15.0
2   14      -1.0          14.0
3   18       4.0          18.0