Creating different types of arrays with conditions, then make an array with the combination of all elements, and finally separate the arrays with a sequence

Suppose,

x and y are two variables. I want to make x number of arrays each containing y elements where each array elements will be multiplied by (1000*x). Then, I want to make an array (say A) with the combination of the x array elements.

For example, x=3 and y=4, then there will be three arays (say a1, a2, a3) each will contain y elements i.e. [1 2 3 4] multiplied by (1000*x).

i.e., for

x=1, a1=[1001 1002 1003 1004]

x=2, a2=[2001 2002 2003 2004]

x=3, a3=[3001 3002 3003 3004]

Now, the array (A) will be the combination of a1, a2 and a3; for instance

A=[1001 2003 2004 3001 3004 1002 2001 2002 1004 1003 3002 3003 ]

(Q1) How can I construct the array A easily?

Later, I want to sequence a1, a2 and a3 based on the sequence of their elements in A.

i.e.,

a1=[1001 1002 1004 1003]

a2=[2003 2004 2001 2002]

a3=[3001 3004 3002 3003]

(Q2) How can I construct a1, a2, a3 from the array A easily?

Answer 1

[Voss]

x = 3;
y = 4;
a = 1000*(1:x).'+(1:y)

a = 3×4

1001 1002 1003 1004 2001 2002 2003 2004 3001 3002 3003 3004

A = a(randperm(x*y))

A = 1×12

2003 3003 3001 1002 2001 2002 1001 3004 2004 1003 3002 1004

[~,idx] = ismember(A,a);
[~,new_idx] = sort(mod(idx-1,x)+1);
a_new = reshape(a(idx(new_idx)),[],x).'

a_new = 3×4

1002 1001 1003 1004 2003 2001 2002 2004 3003 3001 3004 3002