# How to find two arrays of a matrix are equal? and find their location in that matrix??? for example>>> suppose we have a=[1 3 5 6 3 7] how to find which arrays are equal with each other? and find their location??? thank you very much

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vahid torabi on 18 Aug 2014
Commented: Image Analyst on 18 Aug 2014
example:
a=[1 3 5 6 3 7]; how to find that a(2)=a(5)????

Azzi Abdelmalek on 18 Aug 2014
Edited: Azzi Abdelmalek on 18 Aug 2014
a=[1 3 5 6 3 7]
[b,ii,jj]=unique(a)
[freq,idx]=histc(a,b)
location=arrayfun(@(x) find(a==x),b,'un',0)
out=[{'a' 'frequency' 'location'};[num2cell([b',freq']) location']]
Image Analyst on 18 Aug 2014
vahid, the help has all kinds of information on all the functions. You can consult the help for questions like you just asked, and find answers like this:
[C,ia,ic] = unique(A,setOrder) and [C,ia,ic] = unique(A,'rows',setOrder) return C in a specific order. setOrder='sorted' returns the values (or rows) of C in sorted order. setOrder='stable' returns the values (or rows) of C in the same order as A. If no value is specified, the default is 'sorted'.

Image Analyst on 18 Aug 2014
There might be very very many elements that occur more than once in the array. I suggest you call histc() to get a count of all values and see which counts are 2 or greater.
a = randi(9, 1, 100)-5 % Sample data
histEdges = unique(a)
counts = histc(a, histEdges)
% Find locations
for k = 1 : length(counts)
if counts(k) >= 2
locations = find(a == histEdges(k))
end
end