Remove consecutive duplicates from matrix

Hello,

i need to remove duplicates form my matrix, but only if they are consecutive duplicates.

Lets suppose i have the following list of coordinates in a matrix, with for example x, y and z coordinates, that is describing a path.

A=[ 1, 0, 3
    2, 1, 3
    2, 1, 3
    2, 2, 3
    1, 0, 3]

Now, you can see that the point [2, 1, 3] is a consecutive duplicate, that I want to remove (because it's unuseful information).

But I do not want to remove the (duplicate) row at the end, [1, 0, 3], even if this row is already there in the beginning.

Also, the sorting shouldn't be changed. The desired output should be

A=[ 1, 0, 3
    2, 1, 3
    2, 2, 3
    1, 0, 3]

I cannot use 'unique' for that, because that would filter also the last line.

What is the smartest way to do that?

Thank you very much for your help!

Answer 1

[Ameer Hamza]

Try this

A=[ 1, 0, 3
    2, 1, 3
    2, 1, 3
    2, 2, 3
    1, 0, 3];

idx = find(~any(diff(A), 2))+1;
A(idx, :) = [];

[Simon Meyer]

Yes, that works for this example.

Could you explain your answer a little bit so that I wont have problems using this for a much bigger project? :)

Thank you very much!

[Ameer Hamza]

A=[ 1, 0, 3
    2, 1, 3
    2, 1, 3
    2, 2, 3
    1, 0, 3];

First apply the diff() on each column. It calculates difference of consecutive elements

>> diff(A)
ans =
     1     1     0
     0     0     0
     0     1     0
    -1    -2     0

Now I want the rows in which all elements are zero

>> ~any(diff(A), 2)
ans =
  4×1 logical array
   0
   1
   0
   0

the number of rows are one less then the number of rows in A. Since first row can never be removed so I expand the vector like this

>> idx = [false; ~any(diff(A), 2)]
idx =
  5×1 logical array
   0
   0
   1
   0
   0

It shows the rows I want to remove. So I just remove them

>> A(idx, :) = []
A =
     1     0     3
     2     1     3
     2     2     3
     1     0     3

[Simon Meyer]

Thank you very much! :)

[Ameer Hamza]

I am glad to be of help!