[ncl-talk] generate indices for resampling

[Andrew Kren - NOAA Affiliate]

Dear ncl-talk,

This is more of a science question than a coding issue. I noticed ncl has
the function generate_sample_indices to resample with and without
replacement. My data is temperature and moisture retrievals as function of
(time,lev). The issue I am tackling is that my data has a high temporal
frequency. I want to thin the data prior to assimilating it in the HWRF.
The data is reported at approximately every 2-3 seconds for a full 24
hours. So I have a lot of measurements and want to thin it.

I did a test where I retain 80% of the data randomly:

; generate indices for resampling without replacement to sub-sample the
HAMSR data

n_retain = toint(ceil(0.8*dimsizes(time)))

print(dimsizes(time))

iwo = generate_sample_indices(n_retain,0)

print(dimsizes(iwo))


14398 - dimsizes(time)

11519 - dimsizes(iwo)


However, I noticed that maybe this may not be correct since it will only
select n_retain values, and thus may not randomly get indices from the full
dataset to subset. Is there a way to do this with the function without
having to do replacement?


Thanks,


-- 
Andrew Kren
Assistant Scientist
CIMAS & NOAA/AOML
325 Broadway, Boulder, CO 80305
(303) 497-5418
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