Say I have a pd.DataFrame() that I differenced with .diff(5), which works like “new number at idx i = (number at idx i) – (number at idx i-5)”
import pandas as pd import random example_df = pd.DataFrame(data=random.sample(range(1, 100), 20), columns=["number"]) df_diff = example_df.diff(5)
Now I want to undo this operation using the first 5 entries of example_df, and using df_diff.
If i had done .diff(1), I would simply use .cumsum(). But how can I achieve that it only sums up every 5th value?
My desired output is a df with the following values:
df_example[0] df_example[1] df_example[2] df_example[3] df_example[4] df_diff[5] + df_example[0] df_diff[6] + df_example[1] df_diff[7] + df_example[2] df_diff[8] + df_example[3] ...
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Answer
you could shift the column, add them and fill nans:
df_diff["shifted"] = example_df.shift(5) df_diff["undone"] = df_diff["number"] + df_diff["shifted"] df_diff["undone"] = df_diff["undone"].fillna(example_df["number"])