Using unique.m function on NaNs
9 ビュー (過去 30 日間)
Can someone please clarify if the result of unique([1 nan; 1 nan],'rows') should be
a) [1 nan; 1 nan] OR b) [1 nan]
Basically, in my version of matlab (2008b), I get a) as the answer and I think it's a bug as the answer should be b). Can someone please confirm if this is a feature or an issue. My mathworks support is limited because of $$ :(
その他の回答 (3 件)
Jan 2011 年 5 月 17 日
NaNs compared to anything replies FALSE, even NaN==NaN. This is defined by the IEEE754 conventions.
Therefore [1, NaN] compared to [1, NaN] is FALSE also. In consequence UNIQUE([[1, NaN; 1, NaN], 'rows') must reply two rows.
Matt Fig 2011 年 5 月 17 日
In addition to what others have said, note this horribly named function:
A = [1 nan; 1 nan];
Andy 2011 年 5 月 17 日
If you have some application for which you need to ignore NaNs rather than take them into account, you could replace them with some other value which is easily identifiable as non-data. For example:
A; % your data
A(isnan(A)) = Inf; % replace NaN with Inf
A = unique(A,'rows'); % unique rows, where [1,Inf] == [1,Inf]
A(isinf(A)) = NaN; % convert back to NaN
It's a little hackish. I know there are various toolbox functions, like nanmean and nanstd, which calculate other statistics of a dataset while ignoring NaNs. But there is no nanunique or nansort. Also, the work in unique is done by calling sortrows which calls a MEX file, so you can't just edit it to take NaNs into account. So the above code seems like the cleanest quick solution.