Combining year, month, day columns into a single date column with pandas [duplicate]

Answer 1

pd.to_datetime(df[['year', 'month', 'day']])

0   1977-07-17
1   1979-07-15
2   1978-07-26
3   1973-07-16
dtype: datetime64[ns]

If there are invalid combinations you want to NaTify, then add the errors='coerce' argument.