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<p class="MsoNormal">Hi Hoffman<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Thanks for your suggestion – I actually just wrote something similar, except looping through the vertical coords and using ndtooned(). Your method of using reshape() is much more elegant though (albeit with a larger memory burden).<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Thanks again<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Will<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><b><span style="font-size:12.0pt;color:black">From: </span></b><span style="font-size:12.0pt;color:black">Hoffman Cheung <hoffmancheung@gmail.com><br>
<b>Date: </b>Wednesday, 17 October 2018 at 4:52 PM<br>
<b>To: </b>Will Hobbs <will.hobbs@utas.edu.au><br>
<b>Cc: </b>ncl-talk NCL <ncl-talk@ucar.edu><br>
<b>Subject: </b>Re: [ncl-talk] Advice on extracting point locations from array<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><span style="font-family:"Arial",sans-serif">Hi Will,</span>
<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><span style="font-family:"Arial",sans-serif">Given that your 4-D ocean data is T4D(time|nTime,depth|nDepth,lat|nLat,lon|nLon) and you are trying to extract the profile pInd(nProfile,3),</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-family:"Arial",sans-serif">where pInd(:,0), pInd(:,1) and pInd(:,2) corresponds to the index of time, lat and lon dimension, respectively. </span><o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><span style="font-family:"Arial",sans-serif">I would try to do the following way:</span><o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><span style="font-family:"Arial",sans-serif">; rearrange the 4-D ocean data</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-family:"Arial",sans-serif">T4DR = T4D(depth|:,time|:,lat|:,lon|:) ; make sure all dimensions are named </span><o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><span style="font-family:"Arial",sans-serif">; convert the 4-D data into 2-D data</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-family:"Arial",sans-serif">T2D = reshape(T4DR, (/nDepth, nTime*nLat*nLon/))</span><o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">; convert pInd<o:p></o:p></p>
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<p class="MsoNormal">pInd1D = pInd(:,0)*(nLat*nLon) + pInd(:,1)*nLon + pInd(:,2)<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">; extract the profile from 2-D data<o:p></o:p></p>
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<p class="MsoNormal">TProfile = T2D(:,pInd1D)<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">If the above method runs out of memory, you might perform a do loop over the dimension depth, instead of every profile (if you have a huge amount of profiles).<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Regards,<o:p></o:p></p>
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<p class="MsoNormal">Hoffman<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Will Hobbs <<a href="mailto:will.hobbs@utas.edu.au">will.hobbs@utas.edu.au</a>>
<span lang="EN-US" style="font-family:"MS Gothic"">於</span> 2018<span lang="EN-US" style="font-family:"MS Gothic"">年</span>10<span lang="EN-US" style="font-family:"MS Gothic"">月</span>16<span lang="EN-US" style="font-family:"MS Gothic"">日</span><span lang="EN-US">
</span><span lang="EN-US" style="font-family:"MS Gothic"">週二</span><span lang="EN-US">
</span><span lang="EN-US" style="font-family:"MS Gothic"">下午</span>1:53<span lang="EN-US" style="font-family:"MS Gothic"">寫道：</span><o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-US">Hi all</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-US"> </span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-US">This one is for the NCL ‘Brains Trust’. I’m extracting a large number of ocean profiles from a 4-d array (dimensioned time,depth,lat,lon), using coordinate triplets
based on time,lat and lon, (i.e. a 2-d array of indices dimensioned nprofile, 3), but it’s a slow process and I wonder if anyone has any smart ideas on speeding it up.</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-US"> </span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-US">At the moment (partly to manage memory), I’m reading each profile in a loop, viz:</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-US"> </span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-US"> </span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-US">Tprof = new((/nlev,nprofile/),float)</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-US">do i = 0, nprofile-1</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-US"> Tprof(:,i) = fi->T(pInd(i,0),:,pInd(i,1),pInd(i,2)) ;pInd is an array with coord triplets</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-US">end do</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-US"> </span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-US">Obviously one obvious way of speeding things up would be to read the entire array of input data and extract the locations, to avoid multiple i/o calls. What I
really want to do though is somehow get rid of the loop entirely. Is there any way of extracting coordinate pairs (or in this case triplets) without looping through each profile?</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-US"> </span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-US">The only way I can think of is to turn the input array (T in my example above) into a 1-d array, and somehow convert ‘pInd’ into the elements of that 1-d array
– this seems fraught with opportunity for error though. Catastrophic error I can deal with – it’s the sneaky, inobvious error that scares me….</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-US"> </span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-US">Hoping someone has a great idea….</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-US"> </span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-US">Will</span><o:p></o:p></p>
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