CODEWITHSUNDEEP
matlabvectorduplicatesunique
space_voyager
space_voyager

Reputation: 2034

Delete adjacent repeated terms

I have the following vector a:

a=[8,8,9,9,1,1,2,2,3,3,4,4,5,5,6,6,7,7,8,8]

From a I want to delete all "adjacent" repetitions to obtain:

b=[8,9,1,2,3,4,5,6,7,8]

However, when I do:

unique(a,'stable')

ans =

     8     9     1     2     3     4     5     6     7

You see, unique only really gets the unique elements of a, whereas what I want is to delete the "duplicates"... How do I do this?

Upvotes: 2

Views: 316

Answers (1)

Benoit_11
Benoit_11

Reputation: 13945

It looks like a run-length-encoding problem (check here). You can modify Mohsen's solution to get the desired output. (i.e. I claim no credit for this code, yet the question is not a duplicate in my opinion).

Here is the code:

a =[8,8,9,9,1,1,2,2,3,3,4,4,5,5,6,6,7,7,8,8]

F=find(diff([a(1)-1, a]));

Since diff(a) returns an array of length (length(a) -1), we want to add a value at the beginning (i.e the a(1)) to get a vector the same size as a. Here we subtract 1 so that, as mentioned by @surgical_tubing, the command find effectively finds it because it looks for non zero elements, so we want to make sure the value is non zero.

Hence diff([a(1)-1, a]) looks like this:

  Columns 1 through 8

     1     0     1     0    -8     0     1     0

  Columns 9 through 16

     1     0     1     0     1     0     1     0

  Columns 17 through 20

     1     0     1     0

Now having found the repeated elements, we index back into a with the positions found by find:

newa=a(F)

and output:

newa =

  Columns 1 through 8

     8     9     1     2     3     4     5     6

  Columns 9 through 10

     7     8

Upvotes: 4

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