Question

I have a matrix which is a 2d array read from a text file. Each row of text file has 3 entries. The 3rd column has values ranging from 1 to 4. And I want to separate the rows based on this value and put them into different matrix. Could you please suggest a way to do it?

Answer 1

For an Matrix M, as you describe

rowsContainingOne   = M( M(:,3)==1, :)
rowsContainingTwo   = M( M(:,3)==2, :)
rowsContainingThree = M( M(:,3)==3, :)
rowsContainingFour  = M( M(:,3)==4, :)

To see why this works, look at the results from the following portions of:

M(:,3)              %A vector of column three
M(:,3)==1           %A logical array, `true` where column 3 equals one
M( M(:,3)==1, :)    %All columns (indicated by `:`) from rows where the logical array is `true`