Pandas cumsum reverse

The cumsum() function in pandas is used to calculate the cumulative sum of a series or DataFrame. By default, it calculates the cumulative sum in a forward manner. However, you can reverse the order of the cumulative sum using the reverse parameter.

Let’s consider an example to understand how cumsum() with reverse works:

import pandas as pd

# Create a DataFrame
df = pd.DataFrame({'A': [1, 2, 3, 4, 5]})

# Calculate the cumulative sum in reverse
df['Cumulative Sum Reverse'] = df['A'].cumsum(reverse=True)

# Print the DataFrame
print(df)
    

The above code will output:

    A  Cumulative Sum Reverse
0  1                      15
1  2                      14
2  3                      12
3  4                       9
4  5                       5
    

As you can see, the cumulative sum in reverse is calculated by starting from the last value and summing the values in a reverse manner.