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POTrouble in Matlab Preallocating with a Complex For Loop
 

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  1. POTrouble in Matlab Preallocating with a Complex For Loop
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    <p>I am fairly new to matlab but for my job I need to import an ENORMOUS data set and organize it in a certain way. I have written a code that will do this, but very ineffieciently (it is only my third major piece of code and it takes several hours). Matlab is telling me that I can preallocate my variables (about fifty times in fact) but I am having trouble seeing how to do that because I am not sure what matrix the data will be added to for each iteration in the for loop. The code itself probably explains this better than I do.<br> (This is just a small piece of it, but will hopefully display my problem)</p> <pre><code>for x= 1:length(firstinSeq) for y= 1:length(littledataPassed-1) if firstinSeq(x,1)== littledataPassed(y,1) &amp;&amp; firstinSeq(x,2)== littledataPassed(y,2) switch firstinSeq(x,3) case 0 for z= 0:1000 w= y+z; if firstinSeq(x,4)== littledataPassed(w,4) if littledataPassed(w,6)== 1 &amp;&amp; firstinSeq(x,2)== littledataPassed(w,2) &amp;&amp; littledataPassed(w,5)== 0 msgLength0= [msgLength0; firstinSeq(x,:) littledataPassed(w,:)]; break else continue end else msgLength0= [msgLength0; firstinSeq(x,:) [0 0 0 0 0 0]]; break end end case 1 for z= 0:1000 w= y+z; if firstinSeq(x,4)== littledataPassed(w,4) %if sequence not the same, terminate if littledataPassed(w,6)== 1 &amp;&amp; firstinSeq(x,2)== littledataPassed(w,2) &amp;&amp; littledataPassed(w,5)== 0 msgLength1= [msgLength1; firstinSeq(x,:) littledataPassed(w,:)]; break else continue end else msgLength1= [msgLength1; firstinSeq(x,:) [0 0 1 0 0 0]]; break end end case 2 for z= 0:1000 w= y+z; if firstinSeq(x,4)== littledataPassed(w,4) if littledataPassed(w,6)== 1 &amp;&amp; firstinSeq(x,2)== littledataPassed(w,2) &amp;&amp; littledataPassed(w,5)== 0 msgLength2= [msgLength2; firstinSeq(x,:) littledataPassed(w,:)]; break else continue end else msgLength2= [msgLength2; firstinSeq(x,:) [0 0 2 0 0 0]]; break end end for z= 0:1000 w= y+z; if firstinSeq(x,4)== littledataPassed(w,4) if littledataPassed(w,6)== 1 &amp;&amp; firstinSeq(x,2)== littledataPassed(w,2) &amp;&amp; littledataPassed(w,5)== 1 msgLength2= [msgLength2; firstinSeq(x,:) littledataPassed(w,:)]; break else continue end else msgLength2= [msgLength2; firstinSeq(x,:) [0 0 2 0 1 0]]; break end end </code></pre> <p>any thoughts on how I could preallocate these variables(msgLength0,1,2,etc)? They do not have data added for every value in the loop and I am uncertain of the end size for each run. There are a total of eight cases for my switch right now, making this program very slow.</p>
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