We have to take different approach when dealing with time-series data. The fillna() method is used for imputing missing values in such problem.Basic Imputation Techniques:'ffill' or 'pad': Replace NaN values with last observed value'bfill' or 'backfill': Replace NaN values with next observed valueLinear Interpolation method1. Imputing using 'ffill' or 'pad'Code Example:city_day.fillna(method='ff..