Calender month filtering

Below is what I’m able to filter the input file into to 30 days with the command below (GMT6).
gmt filter1d -f0T -Fb30 $input_file -N0 --TIME_UNIT=d -E -V -T$start/$end/30

It would be great if one could do a calendar month filtering, not with the constant interval of 30 days

input_file : 2008-01-16T00:00:00 120.33

Did you try using 1o as the increment and filter width?

I tried using –TIME_UNIT=o
gmt filter1d -f0T -Fb1 $input_file -N0 --TIME_UNIT=o -E -V -T$start/$end/1
Yes, there are differences between the two results. The “-o” option shows consistent time stamp in the result while the time stump for –TIME_UNIT=d varies. See examples of the outputs below:

Also I

  1. output from using the -o1 option
    2008-02-01T00:00:00 129.979
    2008-03-01T00:00:00 122.672
    2008-04-01T00:00:00 135.366
    2008-05-01T00:00:00 133.672

  1. output from using the -d30 option
    2008-02-01T00:00:00 129.979
    2008-03-02T00:00:00 123.212
    2008-04-01T00:00:00 135.366
    2008-05-01T00:00:00 133.672

Not sure which one is correct, though?

Because the nodes of sampling and filtering are different (instead of every 30 days it is 39-31-28 etc) you would expect tiny differences in the filtered values - like here - so I assume this is fine.