Sorting Algorithm

I need to take two arrays and sort one in ascending order, while carrying along the second one. I cannot use the sort function in Matlab.

ex) Array1 = [3,-1,-34,10,8] Array2 = [2,-9,4,-5,0]

Answer 1

[Sean de Wolski]

Then even better - trump your teacher with sortrows!

A = sortrows([array1(:),array2(:)]);
array1_sorted = A(:,1).';
array2_sorted = A(:,2).';

Answer 2

[Andrei Bobrov]

more variant

Array1 = [3,-1,-34,10,8];
Array2 = [2,-9,4,-5,0];
A = [Array1;Array2];
SortedArray = [];
while ~isempty(A)
    [~,I] = min(A(1,:));
    A(:,[1 I]) = A(:,[I 1]);
    SortedArray = [SortedArray A(:,1)];
    A = A(:,2:end);
end

or

Array1 = [3,-1,-34,10,8];
Array2 = [2,-9,4,-5,0];
A =  [Array1;Array2];
k = 1:length(A);
while ~isempty(k)
    [~,I] = min(A(1,k));
    A(:,[k(1) k(I)]) = A(:,[k(I) k(1)]);
    k = k(2:end);
end

or

Array1 = [3,-1,-34,10,8];
Array2 = [2,-9,4,-5,0];
A =  [Array1;Array2];
n = length(A);
for j = 1:n
    k = j:n;
    [~,I] = min(A(1,k));
    A(:,[j k(I)]) = A(:,[k(I) j]);
end

condition without built-in sort functions. I think sortrows, sort and unique - sort function MATLAB

Answer 3

[Matt Tearle]

In the spirit of Sean's answer... this works for the given example:

[~,idx] = unique(Array1);
Array2(idx)

EDIT (and may Cleve have mercy on my soul)

[s1,idx] = unique(Array1);
if numel(s1)<numel(Array1)
    s2 = [];
    for k=1:numel(s1)
        s2 = [s2,Array2(s1(k)==Array1)];
    end
else
    s2 = Array2(idx);
end
s2

[Sean de Wolski]

Unless there are duplicates in Array1.

[Matt Tearle]

"for the given example" :)

Mathematician = badly paid lawyer...

[Sean de Wolski]

touche!

[Matt Tearle]

But since you mention it... [see above edit]

[John D'Errico]

Nah. Mathematician - someone who is good with numbers, but lacks the sheer charisma to be an accountant.

[Buddy Britton]

Matt, I tried running your edited version and there is an error in line 1 "[s1,idx] = unique(Array1)"

[Matt Tearle]

a) Any particular error? Given that it works fine for me (R2011a), it's a bit hard for me to tell why you might be getting "an error".

b) I don't know why you can't use the sort function, but, whatever the reason, I doubt you can really use the unique function either. (Or sortrows)

b, part 2) Sean and I gave answers that technically didn't use sort, but are not good ways to solve the problem (unless there really is a reason you can use unique or sortrows, but not sort).

Answer 4

[Daniel Shub]

I think the sortrows/unique answers may be cheating since they might call sort under the hood ... I am sure this student would not want to cheat. My solution uses both eval and feval, so should get extra credit.

Array1 = [3,-1,-34,10,8];
Array2 = [2,-9,4,-5,0];
while 42 > sqrt(pi)
  eval('x = randperm(length(Array1));');
  if feval('all', diff(Array1(x)) > 0)
    return;
  else
    disp('MATLAB is stupid and guessed wrong!');
    disp(['[', num2str(Array1(x)), '] is not sorted!']);
    disp('Trying again!');
    disp(' ');
  end
end
Array1(x)
Array2(x)

Any concerns about inefficiencies are silly as the distributed computing toolbox would allow my answer to harness the power of a computer cluster.