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how to select the highest values in a 3d file?



Dear Ferret users,

I have a 3D temperature file (lon,lat,time), the time axis representing
200 annual averages. I would like to average the 10 warmest years together for 
each grid point (the selected years will be different from one grid point 
to another). 

Up to now, I did the following: 

use "annual_T_200years.nc"        ---> x=1;97,y=1:24,k=1:200
let Tp=T[d=1]
LET sorted_indices = sortk(Tp)
LET ki = k[k=1:200]
LET sorted_indices_2 = if ki GT 190 then sorted_indices
LET sorted_Tp = samplek(Tp, sorted_indices_2)
LIST sorted_indices_2[x=90W,y=40n,k=189:200], sorted_Tp[x=90W,y=40n,k=189:200]
LIST sorted_Tp[x=90W,y=40n,k=189:200@ave]

LIST sorted_indices_2[x=90W,y=40n,k=189:200], sorted_Tp[x=90W,y=40n,k=189:200]
             Z: 188.5 to 200.5
             LONGITUDE: 90W
             LATITUDE: 39N
 Column  1: SORTED_INDICES_2 is IF KI GT 190 THEN SORTED_INDICES
 Column  2: SORTED_TP is SAMPLEK(TP, SORTED_INDICES_2)
           SORTED_ISORTED_T 
189   / 189:    ....    ....
190   / 190:    ....    ....
191   / 191:   147.0   10.00
192   / 192:     5.0   10.07
193   / 193:   141.0   10.12
194   / 194:   124.0   10.12
195   / 195:    63.0   10.22
196   / 196:     1.0   10.26
197   / 197:     9.0   10.33
198   / 198:    68.0   10.37
199   / 199:    69.0   10.40
200   / 200:   146.0   10.54


LIST sorted_Tp[x=90W,y=40n,k=189:200@ave]
             VARIABLE : SAMPLEK(TP, SORTED_INDICES_2)
             LONGITUDE: 90W
             LATITUDE : 39N
             Z        : 188.5 to 200.5 (averaged)
          10.24

But I cannot do it for ALL gridpoints, since samplek works only with 1D list.

I tried to do a mask:
let test= if k EQ 146 OR k EQ 69 then Tp
"test" provides the 2 temperatures corresponding to the 2 warmest years for 
the point x=90w, y=40n. Unfortunately, I did not find out the general 
command which allows to identify when k is equal to one of the values of 
"sorted_indices_2".
let test= if k EQ sorted_indices_2 then Tp     does not work.

Thank you in advance for any help,
Celine


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