How to part a Matrix into submatrices based on the data

I have a 30.000x5 Matrix, in the third column of each row i have an integer comprised between 1 and 5 and i don't know how many rows there are with each value. I want to divide my matrix into five smaller matrices (Nx5) each of which has into the third column the same value. How do i proceed?

Answer 1

[Fangjun Jiang]

A=magic(5)
a=A(A(:,3)==1,:)
b=A(A(:,3)==13,:)
c=A(A(:,3)>=10,:)

Answer 2

[James Tursa]

E.g., with results in a cell array:

X = the 30000 x 5 matrix
n = number limit for 3rd column
result = cell(n,1);
for k=1:n
    result{k} = X(X(:,3)==k,:);
end

Answer 3

[Star Strider]

If you have R2015b or later, use the splitapply (link) function:

Result = splitapply(@(x){x}, M, M(:,3));

[Matteo Castelli]

What function should i put in splitapply in place of "@(x){x}"?

[Star Strider]

If you just want your ‘M’ matrix separated into sub-matrices for each group identified by an integer in column 3, the anonymous function ‘@(x){x}’ will do what you want. It creates a cell array of sub-matrices with different numbers of rows, each defined by — and with — the integer in column 3.

[Matteo Castelli]

This is what comes out. I am not sure what should i do at this point. P.s. I made a mistake earlier: the coloumn whit the data from 0 to 5 is the second, not the third.

[Star Strider]

I thought they were positive integers. If any are <=0, you need to add a findgroups call first:

[G,ID] = findgroups(Matrix_Dati(:,2));
Result = splitapply(@(x){x}, Matrix_Dati, G);

That should work.