How do I group a list of numbers into different sets in such a way that every set should contain only the identical numbers from the list.

Eg: I have a 2d array as below. [2 1;2 5;2 6;7 8;7 1;7 3;7 2;8 1;8 2]. I would like the output to be three different matrices as below. [2 1;2 5;2 6] [7 8;7 1;7 3;7 2] [8 1;8 2]

I tried out the following: I compared the first coloumn element of each row and after grouping identical numbers, I tried using the 3d array concept. but I get the following error. "Assignment has fewer non-singleton rhs dimensions than non-singleton subscripts" . Kindly request your support