I have a large text file containing numeric data of 1000 groups each of 200 lines. The lines are unsorted. There is a 9 line header at the beginning of each group, i.e., 209 ⨉ 1000 lines altogether.
I want to drop the headers to have a file containing 200 ⨉ 1000 lines. I also want the 200 lines of each output group sorted by the first number in the line. What is a way to do this efficiently in Mathematica?
My actual data set is much larger than 200 lines and 1000 groups. I made up these number for the sake of discussion.