random clustering of any number of rows and columns

 The following code executes  
 A=[0     0    41     0     0;
           0     0     0    42     0];
  non_0=sum(A);
  non_0=repmat(non_0,2,1);
  A_part=[1     2     3     4     5;
          21    22    23    24    25];
  new_A=A;
  new_A(non_0 & A==0)=A_part(non_0 & A==0);

but I want to have for n number of rows and m number of columns and the rows of matrix of A and A_part should be clustered in the  random manner as per the above code mentioned.In addition each cluster can have any number of rows.

[Matt J]

Please indent your code, but not your text. Otherwise, your posts are hard to read.