Remove duplicates and original also

so i'm having trouble trying to eliminate repetitions from my arrays. i've been using unique but can't have the first instance of the element in the return. for example:

A = 1,2,2,2,3,3,3,4,5; B = unique(A); B = 1,2,3,4,5

what i'm actually looking for is B = 1,4,5 where even the first instance of repeating elements is taken out. is this possible?

Thanks

[Declan Bourke]

Hi,

And could i ask quickly, is there any way to do the same with an array of strings? e.g. (AA,AB,AC,AA,AD). I've tried everything I can think of.

Thanks,

Declan

[Stephen23]

See:

https://www.mathworks.com/matlabcentral/answers/298770-removing-duplicate-strings-from-an-array-and-original

Answer 1

[Stephen23]

Assuming that the vector A is sorted:

>> A = [1,2,2,2,3,3,3,4,5];
>> B = unique(A);
>> B(histc(A,B)<2)
ans =
   1   4   5

If A is not sorted, then this is a bit more complicated:

 >> A = [3,3,3,5,1,4,2,2,2,2];
 >> [B,X] = unique(A);
 >> Y = histc(A,B)<2;
 >> A(sort(X(Y))) % in original order
 ans =
     5     1     4
 >> A(X(Y)) % sorted
 ans =
     1     4     5

[Declan Bourke]

Thats a great help, thanks!

Answer 2

[Azzi Abdelmalek]

A = [1,2,2,2,3,3,3,4,5]
b=unique(A,'stable')
c=hist(A,b)
B=b(c==1)

[Declan Bourke]

Thanks for the help!

[Stephen23]

This does not work if A is not sorted into order:

>> A = [3,3,3,5,1,4,2,2,2,2];
>> b=unique(A,'stable');
>> c=hist(A,b)
Error using histc
Edge vector must be monotonically non-decreasing.
Error in hist (line 92)
    nn = histc(y,edges,1);

Although beginners might think that the 'stable' makes a difference, this then provides a non-monotonic sequence to histc, which is not allowed.

Answer 3

[Azzi Abdelmalek]

[ii,jj,kk]=unique(A)
out=ii(accumarray(kk,1)==1)