MATLAB Answers


How to delete repeated rows without using unique function?

Asked by Connor
on 23 Apr 2013

I am looking for a way to delete repeated rows without using the unique function. For example if I have the matrix

A=[2 4 8; 8 2 4; 3 3 -6]

one of the first two rows needs to be deleted. Order doesn't need to be kept. I'm sure I need to use sort, and maybe find or diff. I'm not exactly sure how to go about it.

Any and all help is appreciated!


the cyclist
on 23 Apr 2013

Guessing this is homework. That's the usual motivator for not wanting to use particular functions.

Matt Kindig
on 23 Apr 2013

It's strange that you consider the first two rows of A to be "repeated", since the order of the elements is different (one is a permutation of the other). Is this what you want?

on 23 Apr 2013

They are considered repeated because order isn't important here. This is a very small part for my project, and isn't required. My professor said if we could do this we could get some extra credit. Thanks!


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1 Answer

Matt J
Answer by Matt J
on 23 Apr 2013
Edited by Matt J
on 23 Apr 2013


   >> sortrows(sort(A,2))
ans =
      -6     3     3
       2     4     8
       2     4     8

You should now find diff() rather helpful.


on 23 Apr 2013

I'm still kind of lost where I go from there. Using diff will give me the difference between each element in each row. So when there are three zeros, I know there is a duplicate row. How do I translate that into eliminating a row? I tried using find, but I'm not too familiar with the find function. Thanks for your help.

Cedric Wannaz
on 23 Apr 2013

Lookup ALL and ANY in the doc; you could probably use them at some point, and be aware that ALL, ANY, DIFF, and many others operate along a dimension that you can specify.

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