Unique and Length of every rows of a matrix
1 view (last 30 days)
Show older comments
Hi,
The problem I want to solve is to "filter" the rows of a matrix n x 256. The filter criteria is to keep only the rows where the number of unique elements is between a certain range.
For example, if I have a range of 2:5, and a matrix of double similar to (i know it is not n x 256 for clarity) :
A = [ [1,1,1,4,5,3,3,5,6,1], [2,4,1,5,6,6,6,8,3,2] ... ];
I want to apply unique to every rows of A:
B = [ [1,4,5,3,6], [2,4,1,5,6,7,3] ... ];
Then I want to get the length of every rows of B:
C = [5,7,...];
Then I would like to keep only the rows of A where the corresponding C is in the range. Only the values of C inside the specified range should be kept (ie: 2:5) :
D = [5,...];
I think I could use the indexes of the C matrix that satisfies the criteria to filter A, but I do not know how...
Finally, A would look like :
A = [ [1,1,1,4,5,3,3,5,6,1], ... ];
What would be the quickest way to achieve this? Thank you for your inputs!
J-P
3 Comments
Accepted Answer
Oleg Komarov
on 23 Jul 2011
A = randi([1 256],100,256);
szA = size(A);
B = cell(szA(1),1);
for n = 1:szA(1)
B{n} = unique(A(n,:));
end
C = cellfun('length',B);
idx = ismember(C,100:150); % range 100:150
D = A(idx,:);
2 Comments
Oleg Komarov
on 23 Jul 2011
You could also skip the B{n} and do directly C(n) = numel(unique(A(n,:)) inside the loop, C should be preallocated before as C = zeros(szA(1),1);
More Answers (0)
See Also
Categories
Find more on Creating and Concatenating 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!