MATLAB sorting two vectors by value - matlab

Question

This is a fairly simple task I want to perform, but I can't seem to figure out a way to do it. I've tried sortrows, reshaping, and other solutions, but none of them do exactly what I want.
Essentially, I have two vectors from the same range of values, of unequal lengths. Some of the values are equal, some are not. E.g.
A = [1 5 20 30 53 70 92]
B = [2 3 4 16 20 30 60 95 100]
What I want to do is add "NaNs" to each vector to "stand in" for the values in the other vector that aren't shared. So, I want them to look like:
A = [1 NaN NaN NaN 5 NaN 20 30 53 NaN 70 92 NaN NaN]
B = [NaN 2 3 4 NaN 16 20 30 NaN 60 NaN NaN 95 100]
Some method by which the vector will have placeholders for the value of the other vector.
Do I combine the vectors, sort it, then somehow search and replace all values from the other vector with NaNs? That seems like a bit of a clunky solution, though not impossible. I feel like there is some more elegant way to accomplish this that I am missing.
Thanks!

Answer 1

Here is one solution using a simple map:
A = [1 5 20 30 53 70 92]
B = [2 3 4 16 20 30 60 95 100]
% map all A and B elements
% use 1 for A and 2 for B
map = zeros(max([A,B]),1);
map(A) = 1;
map(B) = bitor(map(B), 2);
% find the values present in either A, or B
[~,~,j] = find(map);
AA = nan(size(j));
BB = nan(size(j));
AA(bitand(j,1)~=0) = A;
BB(bitand(j,2)~=0) = B;
Comparison with Rodys solution shows this method is a bit faster:
A = unique(randi(10000, 1000, 1));
B = unique(randi(10000, 1000, 1));
tic;
for i=1:1000
map=zeros(10000,1);
map(A) = 1;
map(B) = bitor(map(B), 2);
[~,~,j] = find(map);
AA = nan(size(j));
BB = nan(size(j));
AA(bitand(j,1)~=0) = A;
BB(bitand(j,2)~=0) = B;
end
toc
tic
for i=1:1000
C = union(A,B);
Ap = NaN(size(C));
Ap(ismember(C,A)) = A;
Bp = NaN(size(C));
Bp(ismember(C,B)) = B;
end
toc
isequalwithequalnans(BB, Bp)
isequalwithequalnans(AA, Ap)
Elapsed time is 0.283828 seconds.
Elapsed time is 0.457204 seconds.
ans =
1
ans =
1

Answer 2

Well, here's one way:
% union of sets A and B
C = union(A,B);
% initialize new sets, check membership, and
% assign old values when applicable
Ap = NaN(size(C)); Ap(ismember(C,A)) = A;
Bp = NaN(size(C)); Bp(ismember(C,B)) = B;
Note that union gets rid of repititions. In case you want to keep all repetitions, use a manual sort and the second output of ismember:
% combine and sort, KEEPING repetitions
C = sort([A B]);
% initialize new sets, check membership, and
% assign old values when applicable
Ap = NaN(size(C)); Bp = NaN(size(C));
[I,Ab] = ismember(C,A); [I,Bb] = ismember(C,B);
Ap(I) = A(Ab(I)); Bp(I) = B(Bb(I));