# How can I generate a matrix?

3 views (last 30 days)
net on 20 Nov 2013
Commented: net on 20 Nov 2013
Hi, I have two array and I want to generate one matrix according to these arrays.
For example:
a={2,5,2,4,2,3,4,4,8}
b={1,3,1,3,4,2,3,3,2}
Matrix is 2 to 1 -> 1, 5 to 3 -> 1, 2 to 1 -> 2 (again) ...
Output:

Simon on 20 Nov 2013
Hi!
Loop over your a/b vectors and increase the specified matrix element:
M = zeros(max(a), max(b));
for n = 1:length(a)
M(a(n), b(n)) = M(a(n), b(n)) + 1;
end
net on 20 Nov 2013

Laurent on 20 Nov 2013
a={2,5,2,4,2,3,4,4,8};
b={1,3,1,3,4,2,3,3,2};
yourmat=zeros(8,5);
for ii=1:length(a)
yourmat(a{ii},b{ii})=yourmat(a{ii},b{ii})+1;
end
Why are you using a cell array for a and b?
net on 20 Nov 2013
Array "a" is my states and "b" is my observations. I want to know that states and observations amount.
Sorry for my english.
net on 20 Nov 2013
Yes you are right, I wrote with wrong parenthesis. Thanks.

Andrei Bobrov on 20 Nov 2013
Edited: Andrei Bobrov on 20 Nov 2013
a=[2,5,2,4,2,3,4,4,8];
b=[1,3,1,3,4,2,3,3,2];
sz = [8 5];
out = nan(sz + 1);
out(2:end,2:end) = accumarray([a(:),b(:)],1,sz);
out(1,2:end) = 1:sz(2);
out(2:end,1) = 1:sz(1);
Shani on 20 Nov 2013
Andrei do you know about neural networks?
net on 20 Nov 2013