Extracting and formatting data

Hi all,I am trying to do the following: Let's say I have two matrices

A =

           2
           2
           1
           3
  B =

          0.1000
          0.0030
          0.0500
          0.0200
          0.4000
          0.0600
          0.0900
          1.0000

Every value from matrix A represents the number of values I would like to extract from matrix B. For example: if the first value in matrix A is 2, then I would like to extract first two values from B in a row [0.1,0.003] and so on.

[Walter Roberson]

The 2 that is the second value of A: is that also to extract the first two elements of B, or is it to extract the next two elements of B ?

[Doina Gumeniuc]

Hi Walter, first 2 from A means first 2 values from B. Second 2 from A, means the next 2 values from B. So by the time we get to 3 in A, from B we will extract the last 3 values: 0.06, 0.09 and 1. We have 8 values in B, which is 2+2+1+3 in A.

[Rik]

And how did you want to save those different parts?

[Doina Gumeniuc]

Hi Rik! I will fprint them into a vtk input file. In B I have numerous columns so I would like to take it column by column using the same values from A

Answer 1

[Walter Roberson]

B_cell = mat2cell(B, A, size(B,2));

[Doina Gumeniuc]

Hi Walter. This does the job, but how could I extract it in a matrix instead of cell array? On the display I would like to see directly the numbers separated by space. Thank you very much, it would be exteremly helpful!

[Walter Roberson]

http://www.mathworks.com/matlabcentral/answers/304528-tutorial-why-variables-should-not-be-named-dynamically-eval

If it is just a matter of display, you could consider using celldisp()

[Doina Gumeniuc]

Hi Walter, thank you for the link! I have worked it out in the end to get what I need. I have another concern: what if in B I have multiple columns? And I would like to do the same for each. I have first transformed each column in cell with

C=num2cell(B,1);

Then I have tried

B_cell = mat2cell(B{:}, A, size(B{:},2));

But it gives me error :( would it be possible another way? I am trying with cellfun now. I have 50 columns. Thank you very much!

[Walter Roberson]

B_cell = mat2cell(B, A, ones(1,size(B,2)));

[Doina Gumeniuc]

wow..Great, thank you a lot!

Answer 2

[Rik]

A solution that might not scale well, is to convert A to a cell (with num2cell), use cellfun with @(x) 1:x, make sure it is a row array, convert back to a normal vector (with cell2mat) and use that as the index to B (so C=B(index_vector);)