I have a .xls file for each day of the year from 1955 to 2023. The file naming is like: day_1955_1.tif.xls, day_1955_2.tif.xls....so on, 365 files for non leap years and 366 days files for leap years. In naming convention 1955_1, 1955_2, 1955 is the year, and 1, 2 represent day 1(January 1, 1955) and day 2 (january 2).

In these files, I have several columns, but I want to extract only two columns named GROUPED and MEAN.

Then, I want to consolidate these files such that separate columns represent MEAN temperature values for a day of a year, and the column name should include both year and day; this information can be extracted from the file name (Meaning the data should be column-wise). Then I want to save it

Further, I want to aggregate this data yearly for my GROUPED region. The year should also be column-wise.
I tried running the code, but it is not coming in the correct format. Please provide some help in this regard. I have been trying hard since this morning, but I cannot organize and aggregate the data.

I am not able to attach the code here, as it showing some syntex error. Please try to help from the information i have provided in the text.