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From: gcet03 <p.m.somani@gmail.com>
Newsgroups: comp.soft-sys.matlab
Subject: Re: Extracting data
Date: Mon, 29 Dec 2008 23:29:08 -0800 (PST)
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clear all;
b=ones(1,length(a)/4);
c=0;
for i=1:length(a)
    if rem(i,4)==0
        c=c+1;
        b(c)=a(i);
    end
end

Run above code with your values in stored in a variable