Hi Sander,
Thanks again! Using your code, I was able to come further and combine several daily averaged files (tried with 5 daily files in the beginning, everything seemed to be going well), so that’s great!
However, there’s another issue obviously: after generating all 31 daily files for January 2020, I have found I’m not able to combine them, because no output file is generated (and no error message shown). There were several GB free RAM left when harpmerge was running so that should not be an issue. But what then?
I’ve experimented a bit and found that combining my daily files for Jan 1-Jan 24 worked well, but when adding Jan 25, no file was generated anymore. Adding Jan 26 or Jan 27 up Jan1-Jan 24 worked, but adding another file (Jan 28 or Jan 29 or Jan 30 or Jan 31) => again, no output. Then, I removed the added files and went back to Jan 1-Jan 24 and to my huge surprise, haven’t got any output while it worked before. I don’t understand it.
So, what I’ve done for now: I’ve combined the daily files for Jan1-Jan16, and, separately, Jan17-Jan31, and finally, combined these two half-monthly files. Hence, the resulting file will not be exactly the average of all the daily files but the difference should be small enough. But I think this is not how harpmerge is supposed to behave, or at least I haven’t seen any remark on limited number of input files.