Sortrows alternative / matrix sorting

Question

Dan Page 2018-12-12

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/435445-sortrows-alternative-matrix-sorting

编辑： Stephen23 2018-12-13

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

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Answer 1

Stephen23 2018-12-13

1
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https://ww2.mathworks.cn/matlabcentral/answers/435445-sortrows-alternative-matrix-sorting#answer_352155

编辑：Stephen23 2018-12-13

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

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Dan Page 2018-12-13

Thank you

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Answer 2

Bob Thompson 2018-12-12

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/435445-sortrows-alternative-matrix-sorting#answer_352045

编辑：Bob Thompson 2018-12-12

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

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Bob Thompson 2018-12-13

编辑：Bob Thompson 2018-12-13

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 2018-12-13