Find indices of repetitive values

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Mukund
Mukund 2017-11-11
编辑： Jan 2021-10-24
In array a=[1,1,1,2,3,4,3]. I want to find indices of repeating (duplicate) values. Finally want to get the repeating value. Short code with commands such as "unique" and "find" is expected.
  1 个评论
Jan
Jan 2017-11-11
What is the wanted output? Is this your homework? What have you tried so far?

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回答（2 个）

Image Analyst
Image Analyst 2017-11-11
编辑：Image Analyst 2017-11-11
Use findgroups():
a=[1,1,1,2,3,4,3]
groups = findgroups(a)
Then histogram it to find groups with more than 1 count.
Jan
Jan 2017-11-11
编辑：Jan 2021-10-24
With FEX: RunLength:
[B, N, Index] = RunLength(sort(a));
repeated = B(N > 1)
This is the list of values, which occur more than once.
Or:
au = unique(a);
[N, Edge] = histcounts(a, [au, au(end) + 1]);
repeated = au(N > 1)
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Image Analyst
Image Analyst 2017-11-12
mukund, no that does not clarify, it just says what you originally said. So in my example a=[1,1,1,2,3,4,3, 1,4,4,2,2,3] let's consider the 4th 1. Is that a repeat? It's a repeat of the 1's in the first group, but it's in its own group. And the 1 in the second group of 1 is not repeated in its group - there is just one 1, not multiple 1's in the second group. I asked for the output of my example but you did not give it so I don't know how to help you in the general purpose situation.
Mukund
Mukund 2017-11-12
@Jan- Your guess of my expectation is right and this is the required code. Many thanks. I myself tried it in many ways, but no success. Thanks again.
@Image Analyst- Sorry for communication gap from my side. However, Thanks to you for your efforts.

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