Getting error while deleting every row of the matrix M that contains the variable x

1 vue (au cours des 30 derniers jours)
I'm trying to write a function N = Deletevar(x,M) that returns a matrix N by deleting every row of the matrix M that contains the variable x.
My code is :
function N = Delete_var(x,M)
N = [];
[a,b] = size(M);
for i = 1:a
for j = 1:b
if M(i,j)== x
M(i,:)=[];
N = M;
end
end
end
end
However when i call Delete_var(3,[1,2,3;3,4,5;7,8,9]), I get:
Index in position 1 exceeds array bounds (must not exceed 2).
Error in Delete_var (line 9)
if M(i,j)== x
Why is that? How to solve the problem? Please help!
  2 commentaires
David Fletcher
David Fletcher le 1 Mai 2021
Modifié(e) : David Fletcher le 1 Mai 2021
The inherent problem you have with the logic of your code is that you are basing the for loops on the starting size of the array (M). Consider what happens when you delete a row in M - the row dimension becomes smaller, but this is not reflected in the for loop which is still based on the starting size of the array. The code will always ultimately throw an error (unless no rows are deleted) since there will be a mismatch between the starting size of M and its size after rows are deleted.
Ningze Xia
Ningze Xia le 1 Mai 2021
Ohhhh I understand what you mean! Combined your comment and per isakson's answer I successfully solve the problem! Thank you for your help!

Connectez-vous pour commenter.

Réponse acceptée

per isakson
per isakson le 1 Mai 2021
Modifié(e) : per isakson le 1 Mai 2021
The trick is to iterate in reverse order, i.e a:-1:1 instead of 1:a. Try this
%%
M = magic(5);
x = 13;
N = Delete_var(x,M)
N = 4×5
17 24 1 8 15 23 5 7 14 16 10 12 19 21 3 11 18 25 2 9
%%
function N = Delete_var(x,M)
N = [];
[a,b] = size(M);
for i = a:-1:1
for j = b:-1:1
if M(i,j)== x
M(i,:)=[];
N = M;
end
end
end
end

Plus de réponses (1)

Turlough Hughes
Turlough Hughes le 1 Mai 2021
No need for any loops. Here's an example of data to work with
M = randi(10,[10 3]); % sample data
x = 3; % delete rows with this value
You can delete any rows in M containing x as follows:
M(any(M==x,2),:)=[];
  1 commentaire
Ningze Xia
Ningze Xia le 1 Mai 2021
Thank you for your answer! This is a new techinique for me and it's very useful! Really appreciate!

Connectez-vous pour commenter.

Catégories

En savoir plus sur Loops and Conditional Statements dans Help Center et File Exchange

Tags

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by