MATLAB: From a=[1 2 3 4] to b=[1 1 2 2 3 3 4 4]

repelem

code: from a=[1 2 3 4] to b=[1 1 2 2 3 3 4 4]

b = repelem(a,2)

B=A(A(:,1)==1,:);

Lookup "logical addressing" in documentation for details on how this works--it's important Matlab syntax.

Please find the answer of the question asked by me.

Given a=[1 2 3 4 5], generate m=[2 1 3 4 5; 2 3 1 4 5; 2 3 4 1 5; 2 3 4 5 1; 1 3 2 4 5; 1 3 4 2 5; 1 3 4 5 2; 1 2 4 3 5; 1 2 4 5 3; 1 2 3 5 4].

m=[];
k=1;
for i=1:n-1
aa=a;
aa(i)=[];
for j=i+1:n
mm=[];
mm=[aa(1:j-1),a(i),aa(j:n-1)];
m(k,:)=mm;
k=k+1;
end
end