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Topic: Sorting Matrices
Replies: 7   Last Post: Sep 29, 2010 4:33 PM

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Ian

Posts: 14
Registered: 9/21/10
Re: Sorting Matrices
Posted: Sep 29, 2010 4:33 PM
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"Jos (10584) " <#10584@fileexchange.com> wrote in message <i805or$1sm$1@fred.mathworks.com>...
> "Ian " <ikirby23@yahoo.com> wrote in message <i801eh$djr$1@fred.mathworks.com>...
> > "Jos (10584) " <#10584@fileexchange.com> wrote in message <i7vo79$onh$1@fred.mathworks.com>...
> > > "Ian " <ikirby23@yahoo.com> wrote in message
> > > * snip *

> > > > Thanks guys very helpfull so far, I can now find all the consectutive numbers from column 1, the problem I have now is it needs to be sorted providing what the max value is of colum 2, for example:
> > > >
> > > > A=[ 1030 2520
> > > > 1031 2375
> > > > 1315 3618
> > > > 1317 2694]
> > > >
> > > > So for 1030 and 1031 the max value for column 2 is 2520, and for 1315 and 1317 the max value is 3618. I would then want disregard rows 1031 and 1317 and keep 1030 and 1031.

> > >
> > > You have to be a little bit clearer on what you mean by "rows that are consecutive". In my opinion, 1315 and 1317 are NOT consecutive. And you cannot both keep and disregard 1031 (but I assume that is a spelling error ;-) )
> > >
> > > Jos

> >
> > Hi Jos,
> >
> > Sorry I have made a couple of mistakes here, I will try to explain this again a bit clearer. In the matrix below, I want to find the maximum value of column 2 for every consecutive number of column 1.
> >
> >
> > A=[ 1030 2520
> > 1031 2375
> > 1315 3618
> > 1316 2694
> > 1317 2798];
> >
> > So in the matrix there are two sets of consectutive numbers in column 1, 1st set 1030 & 1031, 2nd set 1315, 1316 & 1317. What I want do is find the max value of column 2 for each set of consecutive numbers, so the maximum value for the first set would be 2520 and the maximum value for the second set would be 3618. I would then want to keep the entire row for the maximum values (1030 & 1315) and bin the rest (1031,1316 & 1317).
> >
> > I hope this is a little clearer of what I am trying to acheive, this example is only a little snipit of the data set I am workin with, I need something that will work on a data set which has 4000 rows and 2 columns.

>
> My code in an earlier post does exactly what you're after (i.e. the "keep" part, I am not sure what you mean by "bin the rest") !!
>
> M2 = sortrows(M,[1 -2]) ; % N-by-2 data set
> TF = [true ; diff(M(:,1))>1]
> M2keep = M2(TF,:)
> M2bin = M2(~TF,:)
>
> hth
> Jos


Your code does find the maximum two values for column 2 and gaves you 1315 and 1317, but what I want to do is just find the maximum for each set seperatley, so for rows 1030 & 1031, I want to find the maximum value of column 2, which would only be out of 2520 & 2375, as the maximum would be 2520, I would keep 1030. For the 2nd set 1315,1316 & 1317, I want to be able to find the maximum for these rows only and keep that one, which would be 361 8 (1315). I'm sorry if I'm not explanning this problem very well, but I do appreciate your help.

Thankyou

Ian



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