Selecting elements from a matrix in matlab

Question

I have a matrix which is 36 x 2, but I want to seperate the elements to give me 18, 2 x 2 matrices from top to bottom. Eg if I have a matrix:

1  2
3  4
5  6
7  8
9  10
11  12
13  14
...  ...

I want to split it into seperate matrices:

M1 = 1  2
     3  4

M2 = 5  6
     7  8

M3 = 9  10
     11 12   

..etc.

Answer 1

maybe the following sample code could useful:

a=rand(36,2);
b=reshape(a,2,2,18)

then with the 3rd index of b you can access your 18 2x2 matrices, eg. b(:,:,2) gives the second 2x2 matrix.

Answer 2

I think that the direct answer to your question is:

sampledata = [...
    0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.10 0.11 0.12 0.13 0.14 0.15 0.16 0.17 0.18 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 1.11 1.12 1.13 1.14 1.15 1.16 1.17 1.18; ... 
    0.19 0.20 0.21 0.22 0.23 0.24 0.25 0.26 0.27 0.28 0.29 0.30 0.31 0.32 0.33 0.34 0.35 0.36 1.19 1.20 1.21 1.22 1.23 1.24 1.25 1.26 1.27 1.28 1.29 1.30 1.31 1.32 1.33 1.34 1.35 1.36];

for ix = 1:(size(sampledata,2)/2)
    assignin('base',['M' sprintf('%02d',ix)], sampledata(:,ix*2+[-1 0]))
end

This creates 18 variables, named 'M01' through 'M18', with pieces of the sampledata matrix.

---

However, please don't use dynamic variable names like this. It will complicate every other piece of code that it touches. Use a cell array, a 3D array (as suggested by @Johannes_Endres +1 BTW), or structure. Anything that removes the need for you to write something like this later on:

%PLEASE DO NOT USE THIS
%ALSO DO NOT BACK YOURSELF INTO A CORNER WHERE YOU HAVE TO DO IT IN THE FUTURE
varNames = who('M*');
for ix = 1:length(varNames )
    str = ['result(' num2str(ix) ') = some_function(' varNames {ix} ');'];
    eval(str);
end

I've seen code like this, and it is slow and extremely cumbersome to maintain, not to mention the headache and pain to your internal beauty-meter.

Answer 3

x = reshape(1:36*2,[2 36])'

k = 1
for i = 1:2:35
    eval(sprintf('M%d = x(%d:%d,:);',k,i,i+1));
    k = k+1;
end