Sortrows alternative / matrix sorting

I am trying to make a function to order a 2 row matrix by the top row so that the second row follows the first one. But i am unsure of how to do this. For the challenge i am trying to complete I am not allowed to use the in built sort function.

An example of this is:

INPUT

time = [ 1 3 2 4 7];

signal= [12 14 11 13 16];

Then the function would put this into a 2 row vector it would then be ordered and the output would be:

time_sorted = [ 1 2 3 4 7];

signal_sorted= [12 11 14 13 16];

This is my attempt at this but it isnt working.

Thank you

function [time_sorted,signal_sorted] = mysortdata(time,signal)

%make sure we have more than one element
if numel(time) <= 1
  return
end


timeSignal = [time;signal];

%Picking the end of time to be a place where time is split in two
PivotTime = timeSignal(end);

% Removes this point from time
timeSignal(:,end) = [];
 
%create 4 arrays:
% LessTime/LessSignal: values in the array less than    the pivot
% MoreTime/MoreSignal: values in the array greater than the pivot
LessTime = time(time <= PivotTime);
MoreTime = time(time >  PivotTime);

LessSignal = time(time <= PivotTime);
MoreSignal = time(time >  PivotTime);

%  input Less and More into this function again 
Less = mysortdata(LessTime,LessSignal);
More = mysortdata(MoreTime,MoreSignal);

%Put time back together again
timeSignal(1,:) = [Less, PivotTime, More];



time_sorted = timeSignal(1,:);
signal_sorted = timeSignal(2,:);
 return
end

Answer 1

[Stephen23]

function [A,B] = mysortdata(A,B)
M = qsRecFun([A;B]);
A = M(1,:);
B = M(2,:);
end
function M = qsRecFun(M)
N = size(M,2);
if N>1
    X = fix(N/2);
    S = M(:,[1:X-1,X+1:N]);
    Y = S(1,:) < M(1,X);
    L = qsRecFun(S(:, Y));
    R = qsRecFun(S(:,~Y));
    M = [L,M(:,X),R];
end
end

And tested:

>> T = [ 1, 3, 2, 4, 7];
>> S = [12,14,11,13,16];
>> [Ts,Ss] = mysortdata(T,S)
Ts =
   1   2   3   4   7
Ss =
   12   11   14   13   16

[Dan Page]

Thank you

Answer 2

[Bob Thompson]

I know it may not be the fastest method, but what about using a loop to sort each element. Because you have 'time' and a piece of corresponding data I'm assuming you will always have positive time values, so for each loop you can just pull out the column with the minimum time value into a new matrix, and then remove the column from the original, until you have the whole array sorted.

timesignal = [time;signal];
for i = 1:length(time);
    [value,index] = min(timesignal(1,:));
    sorted(:,i) = timesignal(:,index);
    if index == 1
        timesignal = timesignal(:,2:end);
    elseif index == size(timesignal,2)
        timesignal = timesignal(:,1:end);
    else
        timesignal = timesignal(:,[1:index-1,index+1:end]);
    end
end

[Dan Page]

Hello Thank you for this. But when I try and use it i get:

time_sorted =

     7     5     4


signal_sorted =

     5     9    11

Im not sure how to fix this.

Thank you

[Bob Thompson]

I'm not sure how you're getting that. I did catch one mistake I made with the if conditions, but my results with the test sample you gave came out as you indicate your results should.

[Dan Page]

From sorted i get:

1 2 3 4 4 4 4

3 2 4 7 11 11 11

[Bob Thompson]

Are you using just the code I posted, or did you combine it with something else? That looks like what I would expect, for that particular set of numbers. Did you want them in a different order?

[Dan Page]

it works up to the last 2 colums where it has repeated 4 and 11.