convert an array into its counting sequence..

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?

Answer 1

[madhan ravi]

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

[Jos (10584)]

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 ;-)

[madhan ravi]

I'm not sure either let the OP verify it ;)

Answer 2

[Jos (10584)]

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