Read elements on one side of matrix diagonal into a 1D array
2 views (last 30 days)
Show older comments
Jordan
on 21 Jun 2021
Commented: Scott MacKenzie
on 22 Jun 2021
I would like to read a 2D nxn matrix into a 1D array with only one column. I would like only values on one side of the matrix's diagonal to be put into the resulting array. For example, if there are rows A-D, and columns 1-4 the resulting 1D array would be:
A2
A3
A4
B3
B4
C4
Is there a straightforward way of achieving this? Thank you.
0 Comments
Accepted Answer
Scott MacKenzie
on 21 Jun 2021
Edited: Scott MacKenzie
on 21 Jun 2021
There might be a tighter solution, but I think this achieves what you are after:
a = magic(4)
b = a';
c = logical(triu(ones(4),1));
d = b(c')
Output:
a =
16 2 3 13
5 11 10 8
9 7 6 12
4 14 15 1
d =
2
3
13
10
8
12
2 Comments
Scott MacKenzie
on 22 Jun 2021
The solution is inherently 2D. But, of course, it would work fine in other contexts, such as on a flattened 3D matrix or on individual 2D layers along any dimension of an nD matrix. It will also work, a minor tweak, on rectangular matricies, for example
a = [0 1 2 3 4; 5 6 7 8 9; 4 3 2 1 0]
b = a';
c = logical(triu(ones(size(a)),1));
d = b(c')
Output:
a =
0 1 2 3 4
5 6 7 8 9
4 3 2 1 0
d =
1
2
3
4
7
8
9
1
0
More Answers (0)
See Also
Categories
Find more on Operating on Diagonal Matrices in Help Center and File Exchange
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!