Find non unique string in a table

Hi!

I have a table "TT" which I want to return the "Ticket" of non unique string in the "Alpha".

TT =

  8×2 table
  
  Ticket	Alpha
_______	________
	
29991    	AB'
29991    	CD'
29993    	EF'
30018    	GH'
30066    	IJ'
30105    	KL'
30105    	EF'
30107    	NO' 
  

here EF in not unique under "Alpha" and I want to return "30105". How can i do this?

Answer 1

[Adam Danz]

nonUnqIdx is a logical index of rows of TT.Alpha that are a repeat (ie, not the first instance).

[~, AlphaGroups] = ismember(TT.Alpha, unique(TT.Alpha,'stable')); % identify groups
nonUnqIdx = [1;diff(AlphaGroups)] < 1;

% Tickets for all non-unique (ie repeat) strings in Alpha
TT.Ticket(nonUnqIdx)

Answer 2

[Sean de Wolski]

n = groupcounts(T.Alpha)
[~, last] = unique(T.Alpha, 'last')
T.Ticket(last(n>1))

Using the "new and shiny" groupcounts.

Answer 3

[Sonima]

T.Ticket(groupcounts(T.Alpha)>1)