Inverse of sorting arrangement

[B,I] = sort(A) output is such that B = A(I). What would be the most efficient way to rather get B and J, such that A = B(J)?

Answer 1

[Stephen Cobeldick]

[B,I] = sort(A);
[~,J] = sort(I);
B(J)

Answer 2

[Matt J]

 [B,I] = sort(A); 

 J=1:numel(I);

 J(I)=J;