Problem 661. Spot the outlier

Created by Ned Gulley

Solve Later

All points except for one lie on a line. Which one is the outlier?

Example:

You are given a list of x-y pairs in a column like this:

 pts = [ 0 1 
         0 2 
         3 2
         0 3 
         0 4 ]

You would return the number 3, since the third point is the only one that is non-collinear with the other points. All the others are on the y-axis.

 outlier = 3

Solve

Solution Stats

1929 Solutions
485 Solvers

Last Solution submitted on Jul 10, 2020

Last 200 Solutions

Problem Comments

2 Comments

2 Comments

Justin on 29 Apr 2014

The instructions were a bit confusing at first. It would have been better to say "Find the row number of the outlying point."

Also, using the third row as an answer and a 3 in a column of zeros makes it seem like the intent was to provide unclear instructions. (Or they are just used to writing college textbooks ;) )

Wenwu on 8 Jan 2015

The test set cases 2,3 seems to have two outliers for each case. Please check it

Solution Comments

Solution 2045741

1 Comment

1 Comment

Miles Walker on 4 Dec 2019

Uses the formula for perpendicular distance of a point to a line when the line is not axis orthogonal.

Solution 1015114

2 Comments

2 Comments

Hoai Tran Quoc on 13 Oct 2016

Very interesting, why the test# 3 is not passed. It turned out that the two number
(x4-x1)*(y2-y1) is not the same as (y4-y1)*(x2-x1) due to floating point. I have to compare the subtraction with 10*eps.

Hoai Tran Quoc on 14 Oct 2016

Very interesting. I could not understand why I had not passed the test# 3. It turned out that the two number (x4-x1)*(y2-y1) and (y4-y1)*(x2-x1) are not the same due to floating point. My choice is to compare the absolute difference with 10*eps.

Solution 897667

1 Comment

1 Comment

Francisco on 27 May 2016

I'll try to improve it!

Solution 816895

1 Comment

1 Comment

ABDELRAHMAN on 30 Jan 2016

all tests are solved test3, i don't know what is the problem

Solution 600804

2 Comments

2 Comments

Daniel Pereira on 23 Mar 2015

I'm sorry for this :(

Daniel Pereira on 23 Mar 2015

I got it on solution 600827.
http://www.mathworks.com/matlabcentral/cody/problems/661-spot-the-outlier/solutions/600827

Solution 439564

1 Comment

1 Comment

danteliujie on 28 Feb 2019

great solution

Solution 140502

1 Comment

1 Comment

Jean-Marie Sainthillier on 20 Sep 2012

Doesn't work with outlier in first position.

Solution 97405

1 Comment

1 Comment

Christopher on 11 Jun 2012

Could have been MUCH smaller, but corrcoef doesn't like x=0 the first test case.

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