Counting each day in a dataframe-CodePudding

Say I have a dataframe 'df':

I would like to add an additional column named 'Day No' which adds a count to each day. Desired output below:

This wont reset at the end of each month, the count will just continue. For example at the end of the year it will read 365 for all the 1 hour entries in the last day of the year. The dtype of column 'Datetime' is datetime64[ns].

Any help greatly appreciated, Thanks.

CodePudding user response：

here is one way to do it

# convert to datetime and extract dayofyear

df['Day No']= pd.to_datetime(df['DateTime'], dayfirst=True).dt.dayofyear

PS: if you had shared df constructor or as text, i would have been able to share the result

CodePudding user response：

You can map the result of enumerated unique values:

reversed_dict = dict(enumerate(df['DateTime'].unique(), 1))

df['Day No'] = df['DateTime'].map({v:k for k,v in reversed_dict.items()})