Sorting Matlab Array based on another array

Question

A= [1,  1,  1,  2,  3,  0,  0,  0];
B= [1, 2, 3 , 3, 3 , 4 , 4, 4];

A is the array I have and I want to arrange it so that A would look like:

A= [3,  2,  1,  1,  1,  0,  0,  0]; OR
A= [3,  2,  0,  0,  0,  1,  1,  1];

The point being that I know (from B) there is 1 unique number at the start, then 1 other unique, then 3 unique and another three unique numbers. If A does not fit that profile then I quit. Is there some Matlab function to handle this kind of sorting?

no typo, I know from B that there should be one unique number and 1 other unique number followed by three unique numbers and another three. Each number in B represents 1 unique number, where there are four in total. — user1876942
– user1876942, Commented Sep 9, 2016 at 17:57

Llouis · Accepted Answer · 2016-09-09 19:13:49Z

1

I believe this function is what you are after. It sorts A such that the number of times Asort(i) appears within A matches the number of times B(i) appears within B for all i.

function [ Asort] = numsort( A, B)

A=sort(A);

for i=1:length(A);
numA(i)=length(find(A==A(i)));
numB(i)=length(find(B==B(i)));

end

[numAsort,f1]=sort(numA);
[numBsort,f2]=sort(numB);

if isequal(numAsort,numBsort);
    Asort1=A(f1);
    for i=1:length(A);
        Asort(f2(i))=Asort1(i);
    end

else 
    error('error')    
end

end

Using your vectors A and B, running the function I get:

Asort = [ 2     3     0     0     0     1     1     1 ]

answered Sep 9, 2016 at 19:13

Llouis

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2 Comments

Sardar Usama Over a year ago

seems fine but your else part is incorrect. MATLAB will give error if the condition isequal(numAsort,numBsort) is false. Instead you may want to change else part with this: Asort='error'

Llouis Over a year ago

That was my intention. The point is you can change exactly what the function does during the failure condition, but the function can't return a valid vector.

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