熊猫：无法将日期时间YYYY-mm-dd转换为dd-mm-YYYY

Question

I have a pandas dataframe with column with dates (datetime64[ns] format) The dates are listed as yyyy-mm-dd (like 2018-09-12). I want to convert it to dd-mm-yyyy but what i try doesn't seem to works:

pd.to_datetime(df['date'], format='%d-%m-%Y')
0    2018-09-12
1    2018-09-12

Edit: add example df

df.head(3)
        date      nr
0   2018-09-12   144
1   2018-09-12    37
2   2018-09-12    28

df.info()
date   datetime64[ns]
nr     int

The 'date' doesn't contain any Nan's or Nat's

Answer 1

You need to convert the date parsed with to_datetime to a string in the desired representation. The display format you see right now is the default one used for Datetime objects:

In [10]: frame = {'date': ['2018-09-12', '2016-10-02']}

In [11]: pd.to_datetime(frame['date']).strftime('%d-%m-%Y')
Out[11]: Index(['12-09-2018', '02-10-2016'], dtype='object')

Answer 2

The dates are listed as yyyy-mm-dd (like 2018-09-12).

Yes, but this is not how they are stored. What you are seeing is a specific string representation of datetime objects. Internally, datetime values are stored as integers .

I want to convert it to dd-mm-yyyy but what i try doesn't seem to works

Correct, because pd.to_datetime converts to a datetime object. You need to instead convert your series to a series of strings, which will have object dtype:

df['date'] = df['date'].dt.strftime('%d-%m-%Y')