[ferret_users] seasonal means

[Izidine Pinto <izidinep@xxxxxxxxx>]

Dear ferreters

I have a .nc file (CRU data), which contains monthly climatological values (15-jan-1901,15-feb-1901,16-mar-1901......16-dec-2002) .
I would like to make seasonal climatology (DJF,MAM,JJA,SON)  from 1981 to 1999 and save the result in a single file.
For DJF I did in this way 

set data crutmx.nc
let djf1=cru[l=972:974@ave]
let djf2=cru[l=984:986@ave]
let djf3=cru[l=996:998@ave]
let djf4=cru[l=1008:1010@ave]
let djf5=cru[l=1020:1022@ave]
let djf6=cru[l=1032:1034@ave]
let djf7=cru[l=1044:1046@ave]
let djf8=cru[l=1056:1058@ave]
let djf9=cru[l=1068:1070@ave]
let djf10=cru[l=1080:1082@ave]
let djf11=cru[l=1092:1094@ave]
let djf12=cru[l=1104:1106@ave]
let djf13=cru[l=1116:1118@ave]
let djf14=cru[l=1128:1130@ave]
let djf15=cru[l=1140:1142@ave]
let djf16=cru[l=1152:1154@ave]
let djf17=cru[l=1164:1166@ave]
let djf18=cru[l=1176:1178@ave]

let mean=(djf1+djf2+djf3+djf4+djf5+djf6+djf7+djf8+djf9+djf10+djf11+djf12+djf13+djf14+djf15+djf16+djf17+djf18)/18
save /file=djfcru.nc mean

I have to do for others season.
There are another way of doing this? 

Thanks in advance

-- 
Izidine Pinto
33.55 S 18.22 E