dpb
Posts:
7,885
Registered:
6/7/07


Re: How to remove variable number of rows in each column of a matrix
Posted:
Nov 2, 2013 1:11 AM


On 11/1/2013 11:03 PM, dpb wrote: > On 11/1/2013 9:47 PM, bijan.mobasseri@gmail.com wrote: >> >>> >>> What's the test for determining the starting point for each column? >>  >> They are available separately and known. Let 's say for the 10 >> columns I have 10 numbers. The problem is they are all different. If >> they were the same I would just take off the top of the matrix. > > Then it's just > > result=dat(max(idvec):max(idvec)+499,:); > > You'll want to test that max()+499<length(dat) of course...
Actually, that isn't what you really wanted...probably a case where a simple loop is as efficient as any other solution...
res=zeros(500,size(dat,2)); % preallocate for ix=1:length(idvec) res(:,ix)=dat(idvec:idvec+499,ix); end
accumarray() can do it but probably not any faster than the explicit loop
Again, of course, need the error checking...


