Problem with tuple indices in loop in Python Pandas?

Question

I try to calculate number of days until and since last and next holiday. My method of calculation it is like below:

holidays = pd.Series(pd.to_datetime(["01.01.2013", "06.01.2013", "14.02.2013","29.03.2013",
                                    "31.03.2013", "01.04.2013", "01.05.2013", "03.05.2013",
                                    "19.05.2013", "26.05.2013", "30.05.2013", "23.06.2013",
                                    "15.07.2013", "27.10.2013", "01.11.2013", "11.11.2013",
                                    "24.12.2013", "25.12.2013", "26.12.2013", "31.12.2013",
                                            
                                    "01.01.2014", "06.01.2014", "14.02.2014", "30.03.2014",
                                    "18.04.2014", "20.04.2014", "21.04.2014", "01.05.2014",
                                    "03.05.2014", "03.05.2014", "26.05.2014", "08.06.2014",
                                    "19.06.2014", "23.06.2014", "15.08.2014", "26.10.2014",
                                    "01.11.2014", "11.11.2014", "24.12.2014", "25.12.2014",
                                    "26.12.2014", "31.12.2014",
                                            
                                    "01.01.2015", "06.01.2015", "14.02.2015", "29.03.2015",
                                    "03.04.2015", "05.04.2015", "06.04.2015", "01.05.2015",
                                    "03.05.2015", "24.05.2015", "26.05.2015", "04.06.2015",
                                    "23.06.2015", "15.08.2015", "25.10.2015", "01.11.2015",
                                    "11.11.2015", "24.12.2015", "25.12.2015", "26.12.2015",
                                    "31.12.2015"], dayfirst=True))

#Number of days until next holiday
d_until_next_holiday = []
#Number of days since last holiday
d_since_last_holiday = []

for row in data.itertuples():

    next_special_date = holidays[holidays >= row["Date"]].iloc[0]
    d_until_next_holiday.append((next_special_date - row["Date"])/pd.Timedelta('1D'))

    previous_special_date = holidays[holidays <= row.index].iloc[-1]
    d_since_last_holiday.append((row["Date"] - previous_special_date)/pd.Timedelta('1D'))

#Add new cols to DF
sto2STG14["d_until_next_holiday"] = d_until_next_holiday
sto2STG14["d_since_last_holiday"] = d_since_last_holiday

Nevertheless, I have en error like below:

TypeError: tuple indices must be integers or slices, not str

Why I have this erro ? I know that row is tuple, but i use in my code .iloc[0] and .iloc[-1] ? WHat can I do ?

Can you state your data? Also what is sto2STG14 ? Beside these questions, I thing you should use for row in data.iterrows() and row[1]['Date'] or for i, row in data.row['Date'] as it returns a tuple that does not allow slicing by string. — KaRaOkEy
– KaRaOkEy, Commented Feb 26, 2021 at 8:24
Why convert the list to a pandas object if you're going to iterate through it as tuples? — Paul H
– Paul H, Commented Feb 26, 2021 at 8:33
He is not using the tuples but only wants to access the date. That's why I asked what data is. — KaRaOkEy
– KaRaOkEy, Commented Feb 26, 2021 at 8:34

Wai Ha Lee · Accepted Answer · 2021-02-26 17:26:10Z

With pandas, you rarely need to loop. In this case, the .shift method allows you to compute everything in one go:

import pandas
holidays = pandas.Series(pandas.to_datetime([
        "01.01.2013", "06.01.2013", "14.02.2013","29.03.2013",
        "31.03.2013", "01.04.2013", "01.05.2013", "03.05.2013",
        "19.05.2013", "26.05.2013", "30.05.2013", "23.06.2013",
        "15.07.2013", "27.10.2013", "01.11.2013", "11.11.2013",
        "24.12.2013", "25.12.2013", "26.12.2013", "31.12.2013",
        "01.01.2014", "06.01.2014", "14.02.2014", "30.03.2014",
        "18.04.2014", "20.04.2014", "21.04.2014", "01.05.2014",
        "03.05.2014", "03.05.2014", "26.05.2014", "08.06.2014",
        "19.06.2014", "23.06.2014", "15.08.2014", "26.10.2014",
        "01.11.2014", "11.11.2014", "24.12.2014", "25.12.2014",
        "26.12.2014", "31.12.2014",
        "01.01.2015", "06.01.2015", "14.02.2015", "29.03.2015",
        "03.04.2015", "05.04.2015", "06.04.2015", "01.05.2015",
        "03.05.2015", "24.05.2015", "26.05.2015", "04.06.2015",
        "23.06.2015", "15.08.2015", "25.10.2015", "01.11.2015",
        "11.11.2015", "24.12.2015", "25.12.2015", "26.12.2015",
        "31.12.2015"
    ], dayfirst=True)
)

results = (
    holidays
    .sort_values()
    .to_frame('holiday')
    .assign(
        days_since_prev=lambda df: df['holiday'] - df['holiday'].shift(1),
        days_until_next=lambda df: df['holiday'].shift(-1) - df['holiday'],
    )
)

results.head(10)

And I get:

     holiday days_since_prev days_until_next
0 2013-01-01             NaT          5 days
1 2013-01-06          5 days         39 days
2 2013-02-14         39 days         43 days
3 2013-03-29         43 days          2 days
4 2013-03-31          2 days          1 days
5 2013-04-01          1 days         30 days
6 2013-05-01         30 days          2 days
7 2013-05-03          2 days         16 days
8 2013-05-19         16 days          7 days
9 2013-05-26          7 days          4 days

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