# Is there a way to use find function if I know there will be some empty sets?

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Andrew Poissant on 30 Aug 2017
Edited: Stephen Cobeldick on 31 Aug 2017
I am using matlab's 'find' function below. I get an error saying "Subscripted assignment dimension mismatch," because there are some empty sets in the find solution. I know that 'find' will return an error if it cannot find a solution, but is there a way around this? I simply want a way to use 'find' (or something equivalent) that will not give an error when no sol is found but will instead give an empty set. A simplified version of my code is below where N is a layered 824x824x3 matrix and FGIF is a 936x2 matrix.
[FGIF_r, FGIF_c] = size(FGIF);
tol = 0.00005;
for i = 1:FGIF_r
[row(i), col(i)] = find(abs(N_new(:,:,2) - FGIF(i,1)) <= tol & abs(N_new(:,:,3) - FGIF(i,2)) <= tol);
end

Jan on 30 Aug 2017
I know that 'find' will return an error if it cannot find a solution
No, FIND does not cause an error; when it cannot find a match. It simply replies and empty matrix.
Stephen Cobeldick on 31 Aug 2017
"I know that 'find' will return an error if it cannot find a solution"
Where is that error? I cannot see any error occurring. If find is throwing an error then there is something seriously wrong with your MATLAB installation.
It is not find that has any problems, but your algorithm. So fix your algorithm to correctly handle cases with empty, scalar, and non-scaler outputs from find.
" I simply want a way to use 'find' ... that will not give an error when no sol is found but will instead give an empty set"
>> find(0)
ans = []

Image Analyst on 30 Aug 2017
You could use isempty() to check and do stuff if it's valid and skip it or do other stuff if it's empty.
for i = 1:FGIF_r
expression = abs(N_new(:,:,2) - FGIF(i,1)) <= tol & abs(N_new(:,:,3) - FGIF(i,2)) <= tol;
if ~isempty(expression)
[row(i), col(i)] = find(expression);
else
uiwait(warndlg('Expression is empty'));
% Do whatever you need to do if it's empty....
end
end

Eng. Fredius Magige on 30 Aug 2017
Hi modify and use switch case, as go the second if the first fond empty set ([ ]) Thanks

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Andrew Poissant on 30 Aug 2017