How to convert a column into equal columns

I have a matrix of say:

Number Measurement
  1 0.2
  2 0.5
  3 0.1
  1 0.3
  2 0.2
  3 0.5
  1 0.1
  2 .07
  3 0.9

I want to split this matrix into 3, as in the experiment has been carried out 3 times with 3 measurements each so I can run calculations on each experiment (I actually have a lot more than 3 experiments but they are all of equal number of measurements). I don't need to actually keep the data, I can overwrite the matrix with the one below if I need to as I can save the calculation in another vector. I also don't mind if this is each number is lined up against each other so like this:

1 0.2 1..
2 0.5 2..
3 0.1 3..

etc.

I'be been trying a for i=1:size loop with a nested while number < 4 loop but I hit a problem as the while loop needs to keep running.

Any ideas?

[Azzi Abdelmalek]

This is not clear

Answer 1

[dpb]

>> reshape(reshape(sortrows(d,1),3,[]).',3,[])
ans =
  1.0000    0.2000    1.0000    0.3000    1.0000    0.1000
  2.0000    0.5000    2.0000    0.2000    2.0000    0.0700
  3.0000    0.1000    3.0000    0.5000    3.0000    0.9000
>>

Alternatively, reading the verbiage again, maybe all you're looking for is to get the sets of three one at a time in, say, a loop...

NG=3;  % number per group--use variable to change easily
NE=length(x)/NG         % number experiments in the dataset 
for i=1:NE
  i1=(i-1)*NG;          % first row in the group location
  i2=i*NG;              % last...
  xy=x(i1:i2,:);        % and access that group...
  % do whatever with xy here...
  ...
end

An alternative storage mechanism would be to use a cell array of size NE where each entry is a 2D array holding the data. Then you could loop over it or use cellfun or similar.

Another choice would be a structure array with dynamically named fields of, say 'exp1', 'exp2', etc., for each experiment.

See the documentation on various alternative data structures for more details.