# Replace elements of matrix

조회 수: 4 (최근 30일)
Ionut Anghel 2013년 3월 3일
댓글: Mike Lynch 2020년 11월 24일
I have the folowing:
vector=[1 3 8 9];
matrix=[ 100 1 5 9 6; 100 10 13 3 8; 100 9 10 1 4; ];
% I want to search and replace the vector element with "0"in the matrix (i.e new matrix should be : Newmatrix=[ 100 0 5 0 6; 100 10 13 0 0; 100 0 10 0 4; ]; )
The script is:
Newmatrix=zeros(size(matrix));
for i=1:numel(matrix)
for j=1:length(vector)
valvect=vector(j);
if matrix(i)==valvect
Newmatrix(i)=0;
else
Newmatrix(i)=matrix(i);
end
end
end
The results is not the desired one but:
Newmatrix=100 1 5 0 6
100 10 13 3 8
100 0 10 1 4
So what I'm doing wrong?
Thank you
##### 댓글 수: 1이전 댓글 -1개 표시이전 댓글 -1개 숨기기
Mike Lynch 2020년 11월 24일
The accepted answer or changem are cleaner and more compact, but for the code you wrote the addition of a "break" should fix the problem.
if matrix(i)==valvect
Newmatrix(i)=0;
break
else ...

댓글을 달려면 로그인하십시오.

### 채택된 답변

Youssef Khmou 2013년 3월 3일
hi, try ;
F=matrix;
for i=1:length(vector)
F(F==vector(i))=0;
end
##### 댓글 수: 5이전 댓글 3개 표시이전 댓글 3개 숨기기
Joel Bly 2019년 4월 11일
@BJAnderson how do I change the 1s that come from the ismember function back to the values they are referring to, without changing the zeros?
Walter Roberson 2019년 4월 12일
If you use ismember() with two outputs, then the second output is the index at which the element in the first parameter appears in the second parameter. In places that the element does not occur, then the returned value will be 0 there. You can select just the valid indices by indexing the second output by the first output.
[is_it_there, idx] = ismember(A, B);
idx(is_it_there)

댓글을 달려면 로그인하십시오.

### 추가 답변 (4개)

Metin Ozturk 2018년 8월 1일
The more vectorized and easier way to do this could be as follows:
new_matrix = changem(matrix,zeros(length(vector),1),vector);
##### 댓글 수: 2없음 표시없음 숨기기
BJ Anderson 2019년 3월 12일
YES YES YES. It looks like hardly anyone knows about changem...I see similar questions asked and typically the "solution" involves a loop. A loop in MATLAB is the first sign you're doing something wrong.
changem covers so many situations, and it is elegant and concise, not to mention avoids the risk of re-reassigning an element.
changem is almost always the right anwer. Let the world know!
Thanks Metin for helping to spread the word.
BJ Anderson 2019년 3월 12일
A quick update on changem:
Sadly, if one inspects the actual code within changem, it functions as a loop. While it is a handy one-liner, it does not have the time-savings of moving from a looped function to an matrix-operation function.

댓글을 달려면 로그인하십시오.

Bruno Luong 2019년 3월 12일
F = matrix .* ~ismember(matrix,vector)
##### 댓글 수: 1이전 댓글 -1개 표시이전 댓글 -1개 숨기기
Bruno Luong 2019년 3월 13일
A variant is:
matrix(ismember(matrix,vector)) = 0

댓글을 달려면 로그인하십시오.

Walter Roberson 2013년 3월 3일
Suppose you set Newmatrix to 0 because matrix matched vector(1). Now what happens when you go on to the next j to test if matrix matched vector(2) ?
##### 댓글 수: 0이전 댓글 -2개 표시이전 댓글 -2개 숨기기

댓글을 달려면 로그인하십시오.

Image Analyst 2013년 3월 3일
Try it this way:
newMatrix = matrix % Initialize
for k = 1 : length(vector)
newMatrix(matrix==vector(k)) = 0
end
##### 댓글 수: 1이전 댓글 -1개 표시이전 댓글 -1개 숨기기
Ionut Anghel 2013년 3월 3일
Thanks It is working as well

댓글을 달려면 로그인하십시오.

### 카테고리

Help CenterFile Exchange에서 Resizing and Reshaping Matrices에 대해 자세히 알아보기

### Community Treasure Hunt

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

Start Hunting!

Translated by