Pandas: shift one column until other column value = True

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I have a dataframe like this one:

df = pd.DataFrame(data={
    'date': ['2021-01-01', '2021-01-02','2021-01-03','2021-01-04'],
    'order': [False, False, True, True]
})

And I want to have a new column with the shifted date from the column with the next order = True. So the dataframe would look like this:

df_new = pd.DataFrame(data={
    'date': ['2021-01-01', '2021-01-02','2021-01-03','2021-01-04'],
    'order': [False, False, True, True],
    'shifted_date': ['2021-01-03','2021-01-03','2021-01-04',np.nan]
})
pandas shift dataframe
1 Answers

You can keep the True values with where, fill backwards with bfill, and shift:

df['shifter_date'] = df['date'].where(df['order']).bfill().shift(-1)

output:

         date  order shifter_date
0  2021-01-01  False   2021-01-03
1  2021-01-02  False   2021-01-03
2  2021-01-03   True   2021-01-04
3  2021-01-04   True          NaN
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