How to find the position of the elements of a matrix?
112 views (last 30 days)
Show older comments
giorgos kazas
on 3 Feb 2020
Answered: giorgos kazas
on 4 Feb 2020
I have a 3x3 matrix: J=[0 3 4;3 0 8;4 8 0]
and I want to know in which position the elements exist. For example that 8 exists in second row and third column (2,3) and (3,2) too.
After that I want a new matrix with the value (i.e. 8) in one column and their ''coordinates'' (i.e. 2,3) in a column side by side.
Thanks
2 Comments
Steven Lord
on 3 Feb 2020
Paul Shoemaker's answer will give you the indices of the selected elements in the array, but depending on what you want to do that may not be necessary. For example if you want to get the elements of another array (the same size as J) in the same location as the 8's in J you can do this using logical indexing.
J=[0 3 4;3 0 8;4 8 0]
M = magic(3)
X = M(J == 8)
The vector X contains 9 and 7, the elements from M in locations corresponding to 8's in J. See this documentation page for more information.
Paul Shoemaker
on 3 Feb 2020
Yes, Steven Lord makes a good point: usage may drive you a different way. This is why it's helpful for those posting questions to explain what their end objective is, not just how to perform some specific mechanical action.
Similar to Steven's example, you can also change the original "J" variable where a certain condition is met:
J(J==8) = NaN; % efficient way to change all occurrences of "8" in the original matrix to be NaN's
Paul S
Accepted Answer
Paul Shoemaker
on 3 Feb 2020
Check out the ind2sub Matlab function.
Paul Shoemaker
MatlabInvesting.com
More Answers (1)
See Also
Categories
Find more on Matrices and Arrays 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!