Find indices of repetitive values

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Mukund 2017-11-11

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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.

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Jan 2017-11-11

What is the wanted output? Is this your homework? What have you tried so far?

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Image Analyst 2017-11-11

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https://ww2.mathworks.cn/matlabcentral/answers/366454-find-indices-of-repetitive-values#answer_290578

编辑：Image Analyst 2017-11-11

在 MATLAB Online 中打开

Use findgroups():

a=[1,1,1,2,3,4,3]
groups = findgroups(a)

Then histogram it to find groups with more than 1 count.

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Jan 2017-11-11

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https://ww2.mathworks.cn/matlabcentral/answers/366454-find-indices-of-repetitive-values#answer_290588

编辑：Jan 2021-10-24

在 MATLAB Online 中打开

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)

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 2017-11-12