[ncl-talk] generate_sample_indices without replacement

[Rashed Mahmood]

Hi Sri,
I am not fully sure what your end goal is here. However, if you need to
randomly select 40 members only once then you do not need a loop for it.
Also, if you want to select from 100 members then the function
"generate_sample_indices" should have n=100 instead of 40 that you used.

So if you are interested in randomly selecting *40 members ONLY ONCE *then
your code would be:
Note that I turned OFF the loop because it is not needed for this example.
You can use a loop if you need to randomly select 40 members many times.

;   do j= 0,n-1
     iwo = generate_sample_indices( nens, 0 )
     rcp_40= T2m(:,iwo(0:n-1),:,:)

;   end do


On Thu, Feb 17, 2022 at 8:28 AM Sri nandini via ncl-talk <
ncl-talk at mailman.ucar.edu> wrote:

> Hello dear ncl-users,
>
> I would like to know how to properly code for selecting 40 random
> ensemble from a 100 ensembles of my data.
>
> I wonder if someone could help me with this code? My original data is
> [time | 240] x [ens | 100] x [lat | 180] x [lon | 360]
>
>    f     = addfile ("temperature_data.nc", "r")
>    T2m    = f->temp
>
>    printVarSummary(T2m)
>    dimx = dimsizes(T2m)
>    ntim = dimx(0)          ; 240- time dimension
>    nens = dimx(1)          ; 100- ensemble dimension
>    nlat = dimx(2)            ; 180- lat
>    mlon = dimx(3)          ; 360- lon
>
>    T2m at _FillValue = -9.96921e+36
>
>    ; randomly select 40 members from 100 members without replacement
>    ; define a new variable dimensions
>
>    n=40
>    rcp_40=new((/ntim,n,nlat,mlon/),typeof(rcp45_anom))
>    copy_VarCoords(rcp45_anom(:,0,:,:),rcp_40(:,0,:,:))    ; Copy metadata
>    printVarSummary(rcp_40) ==>Dimensions and sizes:    [time | 240] x
> [40] x [lat | 180] x [lon | 360]
>
>    Coordinates:
>              time: [1192152..1366728]
>              lat: [-89.5..89.5]
>              lon: [   0.. 359]
>
>    do j= 0,n-1
>    iwo = generate_sample_indices( n, 0 )
>    rcp_40(:,j,:,:) = T2m(:,iwo,:,:)  ====>error here fatal:VarVarWrite:
> Number of dimensions on left hand side does not match right hand side
>
>    end do
>    printVarSummary(rcp_40)
>
> Could someone help me in this code?
>
> Best
>
> Sri
>
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