convert an array into its counting sequence..

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VISHWATEJ N
VISHWATEJ N 2019-8-2
编辑： madhan ravi 2019-8-2
i want to convert an array into its counting sequence. for example
if the input is :
x = [1 1 4 4 6 7]
two 1's two 4's one 6 one 7...
output must be :
y=[2 1 2 4 1 6 1 7]
can anyone help?

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回答（2 个）

madhan ravi
madhan ravi 2019-8-2
编辑：madhan ravi 2019-8-2
According to what I understand you want to count the number of occurances of each unique elements in the array x, then:
x = [1 1 4 4 6 7];
[u,~,idx]=unique(x);
v=accumarray(idx,1);
y=reshape([v,u(:)].',1,[])
Gives:
y =
2 1 2 4 1 6 1 7
  2 个评论
Jos (10584)
Jos (10584) 2019-8-2
This fails for inputs like [1 1 2 1 1], where values are repeated.
I admit, the question is a little unclear, but "counting sequence" suggests, at least to me, more than just counting ;-)

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Jos (10584)
Jos (10584) 2019-8-2
This is called run-length encoding, for which there are very efficient functions available on the File Exchange.
https://uk.mathworks.com/matlabcentral/fileexchange?q=run+length+encoding
I point you to my own function RUNINDEX which can also return this:
https://uk.mathworks.com/matlabcentral/fileexchange/56131-runindex
[~, RLE] = runindex(x)
y = reshape(RLE(:,[3 1]).', 1, []) % your format

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