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Hi Billy May be "SAMPLEJ_MULTI" is what you are looking for I could not find its description in documentation page. "sh func SAMPLEJ_MULTI" displays this.. SAMPLEJ_MULTI(J_INDICES,DAT_TO_SAMPLE) Returns data sampled according to J indices which may vary in IKL J_INDICES: ordered indices DAT_TO_SAMPLE: data to sample using J indices Hope it works... Regrads Rahul S Research fellow Indian Institute of Tropical Meteorology Pune, India Rahul > From: william.s.kessler@xxxxxxxx > Subject: [ferret_users] conceptually-simple but oddly-complex sampling problem > Date: Mon, 4 Aug 2014 15:59:30 -0700 > CC: william.s.kessler@xxxxxxxx > To: ferret_users@xxxxxxxx > > Dear expert users :-) > > I have a grid A(y,t) that I want to sample according to a list B(y,t) of J-indices on the identical time axis as A. > That is, I want to extract, at each timestep, the value of A at points B. > Let's say A has shape (Ja,L), and B has shape (Jb,L) > > The output grid I expect would then have the shape (Jb,L); namely, at each timestep, sample the points in A according to the list in B. > > It sounds simple, but actually doing it seems harder. > > What I want is, conceptually: let OUT = samplej(A,B) > But this fails because B is 2-d, and SAMPLEJ requires the list to be 1-d. > > I can do: let OUT = samplej(A,ysequence(B)) > This "works", but OUT now has the shape (Jb*L , L), because ysequence loses the time axis information and I end up with far more points than are justified: samplej has sampled each timestep by the list in B at _all_ timesteps. > > I could do it in a repeat loop: > repeat/range=1:L/name=LL let OUT=samplej(A[l=LL],B[l=LL]) > > Although each repeat step produces a grid of the correct length Jb, I see no way to put the result onto the desired (Jb,L) grid without writing it out and reading it back. > > Anyone have a better idea? > > Thanks ... Billy K > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > William S. Kessler > NOAA / Pacific Marine Environmental Laboratory > 7600 Sand Point Way NE > Seattle WA 98115 USA > > william.s.kessler@xxxxxxxx > Tel: 1-206-526-6221 > Fax: 1-206-526-6744 > Web: http://www.pmel.noaa.gov/people/kessler/ > > |