convert date into day of year in pandas data frame-CodePudding

Got a query! In the given data frame, there is entire column DDAY containing date

   DDAY MM  YYYY
    8   1   1975
    7   2   1978
    14  4   2000
    4   5   2013
    13  10  2018

What is the fastest approach to convert it into day of year?

Thanks!!

CodePudding user response：

Select only columns for convert to datetimes, rename them, so working to_datetime with day, month, year columns and last add Series.dt.dayofyear:

d = {'DDAY':'day','MM':'month','YYYY':'year'}
df['new'] = pd.to_datetime(df[['DDAY','MM','YYYY']].rename(columns=d)).dt.dayofyear
print (df)
   DDAY  MM  YYYY  new
0     8   1  1975    8
1     7   2  1978   38
2    14   4  2000  105
3     4   5  2013  124
4    13  10  2018  286