MATLAB Answers

# Keep track of Matrix row indices after deleting some rows

3 views (last 30 days)
Nadatimuj on 18 Apr 2021
Commented: Nadatimuj on 18 Apr 2021
Suppose, I have a 10x10 Martix A= magic(10).
Then I delete some rows from it as A([3 5 6],:)=[]. and some columns as A(:,[3 5 6])=[]
Now it's a 7x7 matrix.
I want to keep track of the indices to know which row in the orginal matrix becomes which row in the transformed matrix.
A= magic(10);
A([3 5 6],:)=[];
A(:,[3 5 6])=[];
I want to keep track that previous 4th row is now the 3rd row...previous 7th row is now the 4th row...etc. Any solid way to do that? Please help. Thanks.
##### 0 CommentsShowHide -1 older comments

Sign in to comment.

### Answers (1)

KALYAN ACHARJYA on 18 Apr 2021
Edited: KALYAN ACHARJYA on 18 Apr 2021
You can store the A in a temporary variable, and do the modification on temp
temp=A;
Now do the all modification on temp. Result A is original and temp is the modified matrix. Afterwards you can do the comparision between A and temp, like simmilarity
##### 1 CommentShowHide None
Nadatimuj on 18 Apr 2021
Hi,
Thanks for your suggestion. I actually seek help for that "comparison" part. I need to save (for further use) a mapping of new indices that can give me the corresponding old index Matrix row
for example, temp(7,:) and modified(4,:) will give me similar row...I need such index mapping. Thanks.

Sign in to comment.

### Community Treasure Hunt

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

Start Hunting!