Is it possible to sort an array by making the repeated elements in the last?

Question

Mohammad Ayoub 2018-2-21

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https://ww2.mathworks.cn/matlabcentral/answers/383869-is-it-possible-to-sort-an-array-by-making-the-repeated-elements-in-the-last

评论： Mohammad Ayoub 2018-2-21

Greetings.

Consider a vector A = [-2 -2 -1 3 3], is it possible to sort this vector (a generalized method) to [-1 -2 -2 -3 -3]?

The only thing that matters is that the repeated elements are in the last, it doesn't matter what way the repeated elements themselves are sorted (for example, [-1 -2 -2 -3 -3] or [-1 -3 -3 -2 -2] are fine) I just want the distinct value to be on the left before any repeated value.

Thank you in advance,

M. Ayoub

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Answer 1

Stephen23 2018-2-21

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https://ww2.mathworks.cn/matlabcentral/answers/383869-is-it-possible-to-sort-an-array-by-making-the-repeated-elements-in-the-last#answer_306264

编辑：Stephen23 2018-2-21

在 MATLAB Online 中打开

>> A = [-2,-2,-1,3,3,3,9,9,0,99]
A =
   -2   -2   -1    3    3    3    9    9    0   99
>> [cnt,idx] = histc(A,unique(A));
>> [~,idy] = sort(cnt>1);
>> [~,idz] = ismember(idx,idy);
>> [~,ids] = sort(idz);
>> B = A(ids)
B =
   -1    0   99   -2   -2    3    3    3    9    9

And

>> A = [-1,-1,-3,-5,-5]
...
B =
  -3  -5  -5  -1  -1

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Jan 2018-2-21

This sorts in unique, twice in sort and again in ismember. In addition the perfectly working histc is deprecated (what a pity!).

Mohammad Ayoub 2018-2-21

Thank you Stephen and Jan.

Jan I know your answer is true but I think it is a little advanced for me haha, my code is really small and I am still new to MATLAB, so what Stephen wrote works perfectly fine in my application!

By the way, can anyone explain to me what happened exactly (step by step or write the code again with comments) in the code? If you please, so I can understand it better.

Thank you very much!

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Answer 2

KSSV 2018-2-21

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https://ww2.mathworks.cn/matlabcentral/answers/383869-is-it-possible-to-sort-an-array-by-making-the-repeated-elements-in-the-last#answer_306207

在 MATLAB Online 中打开

A = [-2 -2 -1 3 3] ;
s = sign(A) ;
[val,idx] = sort(abs(A)) ;
iwant = s(idx).*val

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KSSV 2018-2-21

What result you expect for [-1 -1 -3 -5 -5]?

Mohammad Ayoub 2018-2-21

The result I expect is [-3 -1 -1 -5 -5] or [-3 -5 -5 -1 -1]

The important thing is that the -3 (which is not repeated) is in the beginning of the array.

By the way, I am limiting my code to 1 repeated value, there will be no more than one repeated element in the arrays (I think this makes it slightly easier)

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Answer 3

Jan 2018-2-21

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https://ww2.mathworks.cn/matlabcentral/answers/383869-is-it-possible-to-sort-an-array-by-making-the-repeated-elements-in-the-last#answer_306277

编辑：Jan 2018-2-21

在 MATLAB Online 中打开

With FEX: RunLength:

A      = [-1 -1 -3 -5 -5];
[b, n] = RunLength(sort(A));
m      = (n == 1);
result = [b(m), RunLength(b(~m), n(~m)];

If you do not have a C-compiler installed, use RunLength_M from this submission.

Maybe this is faster:

sA            = sort(A);
[b, n, index] = RunLength(sA);
mask          = false(size(A));
mask(index(n == 1)) = true;
result        = [sA(mask), sA(~mask)];