Extracting subvector of a vector

Question

I have a set of values (say 20 values) in an array .

 A = [1:20]

I want to divide it in to subsets of known size. If I want to divide it in to 4 sets of size 5 then I can use

y = reshape(A,5,4)'

But my problem is when I dont have matching multiples of sizes. Say I want to divide array in to sets of 3. So there will be 7 sets but the last set will be short.

what exactly I want is

a1= [1 2 3]

a2= [4 5 6]

a3= [7 8 9]

a4= [10 11 12]

a5= [13 14 15]

a6= [16 17 18]

a7= [19 20]

How can I do this kind of subgrouping to a vector in MATLAB?

Answer 1

You can use

y = mat2cell(A,1, diff([0:n:numel(A)-1 numel(A)]));

Then a1=y{1} and so on.

Answer 2

You'll need to write your own function for this. For example:

A = 1:20;
n = length(A);
x = 3;
y = ceil(n/x);
out = cell(y,1);
for i = 1:y
  startIdx = x*(i-1)+1;
  endIdx = min(startIdx + x - 1,n);
  out{i} = A(startIdx:endIdx);
end

Then you can access each row in the cell array:

a1 = out{1};
a2 = out{2}; 
...