How can I detect NaN values in a matrix or vector?

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Doug Hull
Doug Hull 2011-1-18
评论： Fawad Chandio 2019-8-15
How do I identify NaN values?
  1 个评论
Fawad Chandio
Fawad Chandio 2019-8-15
Hello I doing facial recognition attendance system for my final year project I already completed some task but now the problem is that how to recognitions faces...? Help me sir

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采纳的回答

Doug Hull
Doug Hull 2011-1-18
By definition, NaN is not equal to any number, not even NaN itself. Therefore there are two ways to detect NaN values:
% Generate sample data
x = rand(1, 10);
x(x > 0.5) = NaN;
% Find NaN values in two different ways
y1 = isnan(x) ;
y2 = (x ~= x) ;
For speed purposes the use of isnan() tends to be 20%-30% faster. Here's a test snippet if you want to see the comparison:
A = rand(1000); %Random 1000x1000 matrix
A(rand(size(A))>.75) = nan; %Populate with NaNs
t1 = 0; %time of isnan
t2 = 0; %time of ~=
for ii = 1:100
tic
idx1 = isnan(A);
t1 = t1+toc;
tic
idx2 = A~=A;
t2 = t2 + toc;
end
ratio = t2/t1; %ratio of ~= to isnan
isequal(idx1,idx2) %Insure same results
%{
ratio = 1.2179
ans = 1
%}
[From the MATLAB FAQ of Ancient Times...]

更多回答（1 个）

Bozydar Wrona
Bozydar Wrona 2017-6-22
编辑：Bozydar Wrona 2017-6-22
%num is a vector/matrix, if searching for elements different than NaN then:
num(isnan(num)==0)
%otherwise:
num(isnan(num)==1)

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