How to erase data from a matrix from the command line?

INTRO: Hi, I have a matrix Mij and would like to erase the rows i whenever the row-value of two columns are identical (for example:Mi2=Mi3)

Example:

M=3  1.2  13  2
  1.2  0.3  0.3  10
  10  2  1  0
  0.7  5  3  0.4

The new matrix

Nij=  3          1.2  13  2
      10  2  1  0
      0.7  5  3  0.4

I wonder if someone could help me how to solve this issue

Thanks in advance

Emerson

Answer 1

[Matt Fig]

M=[3  1.2  13  2
   1.2  0.3  0.3  10
   10  2  1  0
   0.7  5  3  0.4];

Nij = M(all(diff(sort(M,2),[],2),2),:)

[Emerson De Souza]

Hi Matt Fig,

thank you for your suggestion. You answered exact to the situation: 'whenever the row-value of two columns are identical'. Now, how the command changes if i want to specify two columns, for example: columns 3 and 4? The matrix above will not have any row to erase, but I would like to know how to change the commands.

Thank you in advance for everything

Emerson

[Matt Fig]

You mean you want to delete columns 3 and 4? Or you only want to keep columns 3 and 4?

[Emerson De Souza]

I mean if the row-values of columns 3 and 4 are identical, then erase that row (Not identical row values between columns 2 and 3 as above).

For example, if

M=[3  1.2  13  2
   1.2  0.3  0.3  10
   10  2  1  1
   0.7  5  3  0.4];

then

N=[3  1.2  13  2
   1.2  0.3  0.3  10
   0.7  5  3  0.4];

[Matt Fig]

Same idea:

M = [1 2 3 4;5 6 7 8;1 2 3 3;6 7 8 9;3 4 5 5];
M(~diff(M(:,3:4),[],2),:) = []

[Emerson De Souza]

Now I got it, thank you for your attention

Wish you a nice night

Emerson