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Topic: How to use "Unique"
Replies: 3   Last Post: Nov 12, 2012 1:36 PM

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Doug Schwarz

Posts: 1,412
Registered: 12/7/04
Re: How to use "Unique"
Posted: Nov 12, 2012 12:42 PM
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In article <k7rai0$n1i$>,
"Kevin Ellis" <> wrote:

> Hello,
> I am having trouble figuring out how to use "unique" to find the index of
> identical elements in a single column cell array. As an example, I have a
> cell array with the following data:
> A =
> ''231234242800100043062.68'
> ''231234242800200043208.86'
> ''231234242800400042964.91'
> ''231234242800500038861.19'
> ''231234242800600010255.99'
> ''231234242800900054183.5'
> ''231234242801100077938.9'
> ''231234242801200049682.26'
> ''23123424800900054183.5'
> ''23123424800900054183.5'
> ''23123424GHA0200020256.36'
> I have been trying to use unique to find the index of identical elements. In
> this case, the third and second to last values are equal to one another. I
> need to figure out a way to output the indices 9 & 10. I have tried using
> [C1, ia1, ib1] = unique(A,'first'), but still do not understand how "ib1" can
> be used to find the indices 9 & 10.
> Also, the order is crucial. The order shown in the example cell array cannot
> change. I realize this may be a question for the help file, but after looking
> at it I still do not fully understand so I am hoping someone could help.
> Thanks.
> Kevin

Try this:

[~,~,ib1] = unique(A);
j = find(histc(ib1,1:max(ib1)) > 1);
dupes = find(ismember(ib1,j));

It will find ALL indices of items in A that are duplicated, even if
there is more than one such unique item, i.e., if

A = {'a','a','b','c','c'}

then dupes will be [1 2 4 5];

Doug Schwarz
Make obvious changes to get real email address.

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