Problem 67. Find common elements in matrix rows

Created by Cody Team

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Given a matrix, find all elements that exist in every row.

For example, given

the answer would be the vector '2 5'. Elements should be returned sorted ascending.

Note there is no guarantee that there are any such elements; if there are none, the routine should return the empty set. Also, the matrix might contain NaNs, repeats, or very large or very small elements.

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3787 Solutions
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Last Solution submitted on Jan 17, 2020

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Jason Kaeding on 26 Jan 2012

Any version of "empty" should be acceptable as correct.

For example, intersect can output a 1x0 empty matrix. That should be allowed.

Nils on 22 Oct 2013

Somehow the assert is triggered if the function returns a [] that has been "sorted".
If I include that code
if ~isempty(y)
y = sort(unique(y));
end
no assert is triggered. Seem strange!

Toolman Thoolen on 1 Feb 2018

How can the leading solution be 0??

David Verrelli on 25 May 2018

Following many comments, the Test Suite should be amended to check for an empty output vector using "isempty", rather testing for equality to []. Such an amendment is appropriate, and would not break any of the previously submitted successful solutions. —DIV

Solution Comments

Solution 1868340

1 Comment

1 Comment

SJ Won on 8 Jul 2019

Why doesn't this work?? :( it returns an empty array as I specified...

Solution 1865469

1 Comment

1 Comment

SJ Won on 4 Jul 2019

Why is this incorrect? It's failing when the output is = [];
In matlab, I'm getting output as:
y =
1×0 empty double row vector
Is that not the same thing?

Solution 1669837

1 Comment

1 Comment

ASHOK MALLAGUNTA on 9 Nov 2018

My code is correct but it is showing not a solution.......help me

Solution 1617901

1 Comment

1 Comment

E Chang on 28 Aug 2018

The fact that an empty 0-by-1 matrix does not equal [] is a bit offputting.

Solution 457900

1 Comment

1 Comment

Teemu Pulkkinen on 18 Jun 2014

I had to add an extra if-clause because the assertion isn't particularly forgiving about its definition of an "empty matrix".

Solution 337719

1 Comment

1 Comment

Eli Gershon on 23 Oct 2013

The test suite should consider a 0x0 empty matrix (as given by y = []) as equivalent to a 1x0 empty matrix (which results from the code above it

Solution 216488

1 Comment

1 Comment

Dirk Engel on 12 Mar 2013

solution uses recursion

Solution 210527

1 Comment

1 Comment

Bishes Rayamajhi on 28 Feb 2013

nice !!!

Solution 101651

2 Comments

2 Comments

Christopher on 22 Jun 2012

argh! trying to debug third test case. I am returning a []. assert is comparing that to a []. How do I fail?
Both 3rd test case and 5th evaluate to [] locally, but I fail the cody asserts.

David Verrelli on 25 Sep 2017

As others have later commented, the assert requires a 0×0 size 'empty' vector. See edited version in Solution 1276044.

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Problem 67. Find common elements in matrix rows

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Problem 67. Find common elements in matrix rows

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