Problem 7. Column Removal

Created by Cody Team

Solve Later

Remove the nth column from input matrix A and return the resulting matrix in output B.

So if

 A = [1 2 3;
      4 5 6];

and

 n = 2

then B is

 [ 1 3  
   4 6 ]

Solve

Solution Stats

Last solution submitted on Aug 19, 2019

Last 200 Solutions

Problem Comments

14 Comments

14 Comments

Show 11 older comments

Jon on 13 Nov 2013

All solutions with score 11 or 12 use the regexp cheat.

Len on 11 Sep 2014

Is there somewhere to go to receive advice on how to improve your code?

Sneha on 30 Oct 2014

Is there somewhere to go to receive advice on how to improve your code?

Salil Goel on 17 Mar 2015

i can't think of a better solution having size less than 19!

Nicholas Hind on 21 Apr 2015

why isn't B = (A(:,n)=[]); working? thanks

Jyotsna mallela on 8 Jun 2015

How to improvise this code?

Noriko Hounoki on 7 Dec 2016

It's very MATLAB!

Raynald Belmont on 18 Dec 2016

this was actually not that difficult :)

Rasheed Abid on 31 Jan 2017

a good way to learn

David Verrelli on 19 Mar 2017

There should be a single-column input matrix in the test suite.

Mohsen Khodadadi on 29 Mar 2017

This was fun! Not difficult, but kind of challenging!

cqut on 22 Dec 2017

A(n,:)=[]; B = A; it works,but I'm wrong,who tell me the reason?

Varun Garg on 7 May 2018

Better test cases could be provided for edge cases.

Ashish Khulbey on 26 Jul 2019 at 10:01

Great problem.
Lets you dug deep into the documentation for an awesome solution.
This link might help : https://in.mathworks.com/help/matlab/math/removing-rows-or-columns-from-a-matrix.html

Solution Comments

Solution 1673559

1 Comment

1 Comment

Carlos Castillo on 14 Nov 2018

B = horzcat(A(1:end,1:n-1), A(1:end,n+1:end)); gives size 35.

How can we know the real leading solution sizes if there are those "message solutions" that are not real solutions?

Solution 1453889

1 Comment

1 Comment

Yanni Wang on 3 Mar 2018

woooooooow! good job

Solution 1444480

1 Comment

1 Comment

Aamod Garg on 20 Feb 2018

I really need to learn to code better. I say this because I keep on getting size which is atleast 2-3 times the size of the leading solution.

Solution 1212791

1 Comment

1 Comment

John Badawi on 15 Jun 2017

larger size but will work for n=1

Solution 1212790

1 Comment

1 Comment

John Badawi on 15 Jun 2017

This would fail for n=1

Solution 1101481

2 Comments

2 Comments

SIVAPRAKASH DANABALASINGAM on 10 Jan 2017

VERY EASY

Josiah Swim on 29 Mar 2017

good stuff

Solution 1101473

1 Comment

1 Comment

Devan Rao on 10 Jan 2017

good

Solution 1093335

1 Comment

1 Comment

Eqin Azlan on 29 Dec 2016

B(n)=A[] ?

Solution 986730

1 Comment

1 Comment

Coen Beeksma on 29 Sep 2016

What am I doing wrong? Im new btw. Learning the basics.

Solution 953840

1 Comment

1 Comment

Mohit Verma on 2 Sep 2016

What is the best optimized solution for this particular problem? Could someone with size 19 or smaller please indicate their solutions. Thanks

Solution 781048

1 Comment

1 Comment

Gunvor Røkke on 19 Nov 2015

My code solves the problem, yet I get incorrect answer

Solution 716320

1 Comment

1 Comment

Ruchika Soni on 19 Aug 2015

Good one.

Solution 587900

1 Comment

1 Comment

Hiroki Fujiwara on 25 Feb 2015

no need to use for loop or anything.
it's just this.

Solution 540022

2 Comments

2 Comments

Stephen on 4 Dec 2014

nice, I wish I had thought of it this way

VOXEL INFOTECH Chennai-IND on 4 Dec 2014

nice

Solution 535203

2 Comments

2 Comments

VIVEK RUHELA on 25 Nov 2014

can anybody tell me why this solution is not working:"[a,b] = qr(A);
[a1,b1] = qrdelete(a,b,n);
y = a1*b1;"
Although it gives right answers to all test Suits in the software.Plz

Zikobrelli on 27 Nov 2014

because of rounding errors.
B = round(a1*b1);
it should work in this case as all numbers are integers.

Solution 534945

2 Comments

2 Comments

Christopher Zerafa on 24 Nov 2014

B=A(:,1:end-1);

What is wrong here?

Tanguy on 28 Jan 2015

you are just removing the "last" column, not the "n-th" column.

Solution 528077

1 Comment

1 Comment

VIVEK RUHELA on 13 Nov 2014

I've checked this coding:"[a,b] = qr(A);
[a1,b1] = qrdelete(a,b,n);
B = a1*b1;" Why this not working??? Can anybody check this....

Solution 513186

1 Comment

1 Comment

Abdul on 16 Oct 2014

Hi, this code working good. then how to say it is incorrect?

Solution 290589

1 Comment

1 Comment

Pascal COMBES on 26 Jul 2013

Why the following solution doesn't work? It does on my MATLAB 2011a :

function B = column_removal(A,n)
if((n < 1) || (n > size(A, 2)))
B = A;
return;
end
if(n > 1)
l = A(:, 1:(n-1));
else
l = [];
end
if(n < size(A, 2))
r = A(:, (n+1):size(A, 2));
else
r = [];
end
B = [l,r];
end

Solution 262370

2 Comments

2 Comments

MKN on 19 Jun 2013

Well done!!

Huy on 11 Aug 2013

Ditto

Solution 213942

1 Comment

1 Comment

Adrian Dronca on 7 Mar 2013

oops ! didn't read the requirements right

Solution 213732

1 Comment

1 Comment

Adrian Dronca on 8 Mar 2013

i`m not really sure [] is faster than '' but is good to know

Solution 175158

1 Comment

1 Comment

sea knowledge on 12 Dec 2012

it seems that A(:,n)='' is a bit faster than A(:,n)=[]; but usually we use the latter one,

Solution 134992

1 Comment

1 Comment

Daniel Cook 10 hours and 44 minutes ago

I can't believe it is this simple. lol.

Solution 126061

5 Comments

5 Comments

Show 2 older comments

Sadid on 15 Aug 2012

Dear Oscar,
in comparison to your code, the below implementation is much faster but your style of code is a crack to cody system, well done.

function A = column_removal(A,n)
A(:,n) = '';
end

Óscar on 16 Aug 2012

Dear Sadid, I agree with you that my implementation is completely stupid and a waste of time in real life and that's why I don't like the current evaluation metric of Cody. A (time and/or memory)-based evaluation would be much more interesting. With the current evaluation metric, Cody promotes hacking and cracking (which is also fine), but players don't learn good manners for developing efficient code.

ahmed bilal on 16 Oct 2012

NICE ONE BUT BIT DIFFICULT

HaveF on 17 Dec 2012

@Óscar yes, you are right. the player can't study the one with well written style

PARTH PATEL on 16 Sep 2014

agreed with Oscar

Solution 71383

1 Comment

1 Comment

tomio wakasugi on 5 Apr 2012

My MATLAB 2012a worked for #2

Solution 60410

6 Comments

6 Comments

Show 3 older comments

Craig on 13 May 2012

What happened to "and return the resulting matrix in output B"?

Dirk Engel on 22 Jun 2012

Strange: A(:,n) = [] has size 15 but is basically the same?

Andrew on 16 Jul 2012

How safe is this to do?

Mechatrobrnotronik on 2 Mar 2013

function ans = column_removal(A,n)

A(:, n) = ''
end

Why doesn't this code work? :/

Florian M. Faessler on 27 Oct 2013

@Mechatrobrnotronik: I tested your code.
function ans = test_fkt(A,n)
A(:,n) = ''
end
Works for me. Returning A with removed column n.
Nonetheless I am interested in what '' actually does. I couldn't find it in the command reference.

Kristin Foster on 3 Dec 2017

fun

Solution 1122

2 Comments

2 Comments

Yi Cao on 25 Jan 2012

Can the server provide more information on failed solution?

Ninetrees on 9 Feb 2012

For those who wonder how such low scores are being reported in Cody, it is because many players are changing the actual function call. The result is obvious to those of us who have solved many of these challenges.

Problem 7. Column Removal

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Problem 7. Column Removal

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Recent Solvers13555

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