Error in For Loop

Hi everybody,

I have code given below, num is a 1500x3 sized matrix and it has class labels in its third column and number of the classes labels are change according to the input value . I want to keep each line in the class matrix in certain places by class number like Class 1 will be held between 1 and 400 lines,Class 2 will be held between 401 and 790 lines etc. but code gicen below always writes the values same lines

clc; clear all;
[num,txt,raw]    = xlsread('data-1.xlsx');
k                = input ('Enter a k value:');

 for d =1:k ;
        lclass                     = length(num(num(:,3)==d,1:2));
        a(d+1)                     = lclass;
        class(:,1:2)               = [num(num(:,3)==d,1:2)];
        
 end

Answer 1

[David Hill]

class=[];
for d =1:k ;
        class= [class,num(num(:,3)==d,1:2)];
end

[David Hill]

class=[];
for d =1:k ;
        class= [class;num(num(:,3)==d,1:2)];%needs to be ;
end

[Ararat Cetinkaya]

with using this expression 'class=[];', did we assignme a matrix to class variable ?

[David Hill]

Yes, an empty matrix

[Ararat Cetinkaya]

it helped me a lot thanks for your help.