Using python and Pandas to write a function that: For each value, count the difference back to the previous zero (or the start of the Series, whichever is closer) create a new column 'Y' Consider a DataFrame df where there is an integer column 'X' import pandas as pd df = pd.DataFrame({'X': [7, 2, 0, 3, 4, 2, 5, 0, 3, 4]})