How to get monthly average temperature data from daily temperature data in new columns at the end by month name?

I have a yearly mean temperature data from 1989 to 2019, the table headers are named Day_1 to Day_365, I want to get monthly data in new column with month name and automate the process to get for all years from 1989 to 2019.

Please Help.

[Akira Agata]

You mean, you have a temperature data like the following:

Year Day_1 Day_2 ... Day_365 Day_366

---- ----- ----- ... ------- -------

1989 10 20 ... 20 nan

... ... ... ... ... ...

1992 10 20 ... 20 15

... ... ... ... ... ...

And want to add 12 new columns representing monthly average for each year, like the following ?

Year Day_1 Day_2 ... Day_365 Day_366 Avg_Jan ... Avg_Dec

---- ----- ----- ... ------- ------- ------- ... ------

1989 10 20 ... 20 nan 15.1 ... 11.1

... ... ... ... ... ... ... ... ...

1992 10 20 ... 20 15 15.3 ... 11.3

... ... ... ... ... ... ... ... ...

[Saranga Bordoloi]

Lat Long Day_1 Day_2 ... Day_365 Day_366

---- ----- ----- ----- ... ------- -------

26.5 97.5 10 20 ... 20 nan

... ... ... ... ... ...

27.5 98.5 10 20 ... 20 15

... ... ... ... ... ... ...

And want to add 12 new columns representing monthly average for each points in a new table

Lat Long Day_1 Day_2 ... Day_365 Day_366 Avg_Jan ... Avg_Dec

---- ----- ----- ... ------- ------- ------- ... ------

26.5 98.5 10 20 ... 20 nan 15.1 ... 11.1

... ... ... ... ... ... ... ... ...

27.5 98.5 10 20 ... 20 15 15.3 ... 11.3

... ... ... ... ... ... ... ... ...

But for rainfall data i need the total rainfall(jan 1+...Jan 31) of the month not the average

Lat Long Day_1 Day_2 ... Day_365 Day_366 total_Jan ... total_Dec

---- ----- ----- ... ------- ------- ------- ... ------

26.5 98.5 10 20 ... 20 nan 50 ... 80

... ... ... ... ... ... ... ... ...

27.5 98.5 10 20 ... 20 15 75 ... 140

... ... ... ... ... ... ... ... ...

I have this kind of data from year 1989 to 2019

After taking out the Monthly averages(temperatures) & rainfall (total);

i want to again calculate the average of January 1989, January 1990,...January 2019; and but this time average of rainfall of january 1989 to january 2019.

Lat Long jan Feb ... Nov Dec

---- ----- ----- ... ------- -------

26.5 98.5 10 20 ... 20

... ... ... ... ... ...

27.5 98.5 10 20 ... 20

... ... ... ... ...