[ferret_users] Extracting the maps for certain months to a separate data set

[Alejandro Ludert <aludert@xxxxxxxxxx>]

Dear Ferret community:

My problem is as follows; I have a data set of monthly mean maps of rainfall anomalies and wish to extract the maps of December, January and February to a separate data set. I have done it like this:

save/clobber/file=precip.nc precip[l=1:3]

save/append/file=precip.nc precip[l=13:15]

save/append/file=precip.nc precip[l=25:27]

save/append/file=precip.nc precip[l=37:39]

save/append/file=precip.nc precip[l=49:51]

save/append/file=precip.nc precip[l=61:63]

save/append/file=precip.nc precip[l=73:75]

save/append/file=precip.nc precip[l=85:87]

save/append/file=precip.nc precip[l=97:99]

save/append/file=precip.nc precip[l=109:111]

save/append/file=precip.nc precip[l=121:123]

save/append/file=precip.nc precip[l=133:135]

save/append/file=precip.nc precip[l=145:147]

save/append/file=precip.nc precip[l=157:159]

save/append/file=precip.nc precip[l=169:171]

Which apart from being not at all elegant has the problem of adding a blank (missing value) data point in between each set of three months, something like this. From what I read it has to do with how ferret appends data to a data set when the time axis end of the old data and beginning of new data don't match. 

01-DEC-1979 00 /  1:  0.0780

 01-JAN-1980 00 /  2: -0.2193

 01-FEB-1980 00 /  3: -0.2447

 01-JUL-1980 18 /  4:    ....

 01-DEC-1980 00 /  5: -0.4120

 01-JAN-1981 00 /  6: -0.4793

 01-FEB-1981 00 /  7: -0.2847

 02-JUL-1981 00 /  8:    ....

 01-DEC-1981 00 /  9:  0.0980

 01-JAN-1982 00 / 10: -0.1393

 01-FEB-1982 00 / 11: -0.2347

 02-JUL-1982 00 / 12:    ....

 01-DEC-1982 00 / 13:  0.5380

 01-JAN-1983 00 / 14: -0.5393

 01-FEB-1983 00 / 15: -0.5347

 02-JUL-1983 00 / 16:    ....

How can I save the maps for only the months I am interested in without having these extra data point in between? And in a related note, After I finish my EOF analysis, how can I tell ferret that the data points i'm trying to plot correspond to D-J-F of each year i.e. 39 data point in total each corresponding to D-J-F from 79-80 to 93-94 and to plot them omitting the spaces in between.

Thank you very much in advance and if you need an example of my data let me know.

Thank you again. Alejandro Ludert.