{Timestamp('2016-11-06 10:00:00'): ['Item1', 'Item3', 'Item4'], Timestamp(
    '2016-12-06 12:00:00'): ['Item1'], Timestamp('2016-12-06 10:00:00'): [
    'Item1', 'Item3', 'Item4'], Timestamp('2016-12-06 11:00:00'): ['Item1',
    'Item2']}
print(df.groupby(df['date'].dt.round('d')).Item.apply(lambda x: x.unique().
    tolist()).to_dict())
{Timestamp('2016-11-06 00:00:00'): ['Item1', 'Item3', 'Item4'], Timestamp(
    '2016-12-06 00:00:00'): ['Item1', 'Item2', 'Item3', 'Item4']}
Pandas groupby hour of the day to dictionary