For consistency with "nan", wouldn't it be nice to be able to issue "missing(3)"?

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FM 2022-4-26

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https://ww2.mathworks.cn/matlabcentral/answers/1705790-for-consistency-with-nan-wouldn-t-it-be-nice-to-be-able-to-issue-missing-3

评论： Bruno Luong 2022-4-27

<Missing> is the string counterpart to NaN. One can define a (say) 3x3 array of NaN's. Each NaN can be replaced as the data is generated in the analysis process, which is handy if the data isn't generated simultaneously. At no point is there any confusion between NaN versus a valid zero datum.

It would be nice to be able to do this for strings. Of course, one can issue "string(nan(3))" or "repmat(missing,3,3)". But as code gets more intricate, simplicity becomes more valuable.

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FM 2022-4-26

编辑：FM 2022-4-26

At least for me, syntatic sugar has a very real impact when it comes to quickly and consistently modifying code during exploratory analysis. I'm using exactly the same equivalence checking syntax as for numbers. When iterating over a horizontal vector of strings, I don't need to unpack the string from a cell. Within general purpose utility functions, I don't need to test a variable to see if it needs special handling. The last thing I need is for a function written months or years ago to break because the code didn't account for the special syntax of strings. I then have to rip my mind away from what it was doing and descend into the minutiae of that code, hoping that I don't break anything else by modifying it.

Just to bring the discussion back on course, this question isn't about whether strings should be supported. It is about making the behaviour cleaner and more consistent with numbers.

But in response to questions about x+pi, you would probably instead do disp("The matching records in JoinTable = "+sum(BinaryMaskingVector)). It's more readable than the traditionan fprintf, though nothing prevents you from resorting to the latter when it is more advantageous.

FM 2022-4-27

@Jan: In 2019a, missing(2,3) and missing(2,3,'string') are not recognized. I'm still waiting to upgrade. The command "doc missing" yields a very sparse documentation page....

Jan 2022-4-27

在 MATLAB Online 中打开

@FM: In R2022a this syntax is not working also - you can try this here in the forum's interpreter:

missing(2,3,'string')
Error using missing
Too many input arguments.

So this is a useful enhancement request. Please use the link on the bottom of this page to contact the MathWorks team and suggest this improvement.

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回答（1 个）

Bruno Luong 2022-4-27

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https://ww2.mathworks.cn/matlabcentral/answers/1705790-for-consistency-with-nan-wouldn-t-it-be-nice-to-be-able-to-issue-missing-3#answer_951775

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Why not define your own function

mymissing
ans = missing
    <missing>
mymissing(3)
ans = 3×3 missing array
    <missing>    <missing>    <missing>
    <missing>    <missing>    <missing>
    <missing>    <missing>    <missing>
mymissing(2,3)
ans = 2×3 missing array
    <missing>    <missing>    <missing>
    <missing>    <missing>    <missing>
mymissing(2,'string')
ans = 2×2 string array
    <missing>    <missing>
    <missing>    <missing>
mymissing(2,3,'double')
ans = 2×3
   NaN   NaN   NaN
   NaN   NaN   NaN
function x = mymissing(varargin)
% x = mymissing(size)
% x = mymissing(n1, n2, ...)
% x = mymissing(..., class)
x = missing;
if ~isempty(varargin)
    if ischar(varargin{end}) || isstring(varargin{end})
        sz = [varargin{1:end-1}];
        if isempty(sz)
            sz = 1;
        end
        cls = varargin{end};
        x = repmat(feval(cls,x), sz);
    else
        sz = [varargin{1:end}];
        x = repmat(x, sz);
    end
end
end

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FM 2022-4-27

编辑：FM 2022-4-27

Thanks, Bruno.

I know what I'm going to say is obvious, but a simple way would be missing(nan(3)) or repmat(missing,3,2). The functionality wasn't the point so much as consistency. We have a thing called "missing", and having it behave in the same way as NaN (or zeros or ones) would streamline the language.

It wasn't until Jan posted the "missing" constructor that I realized it has become more complicated after 2019a. The doc page for 2019a says that "missing" is the string counterpart to NaN for doubles, but if missing(2,3,'string') works for later versions of Matlab, then it has become a more general generator of indicators of absent data for more than just strings.

My 2019a doesn't have such constructor behaviour, so I can't play with it and scope out what the behaviour is. I thought the constructor returned a string (in the same way that NaN is considered to be a double), but even on my 2019a, class(missing) returns 'missing'. It is its own special class with its own behaviour.

For example, x=repmat(missing,3,3);x(2,2)=pi causes an error converting pi to "missing", but x=ones(3);x(2,2)=missing is fine.

Because of its exceptional behaviour, I'm not sure if it makes sense to allow missing(3) as opposed to string(nan(3)).

FM 2022-4-27

@Bruno Luong: No, I should have been clearer. the 2019a documentation for "missing" does not describe it a specific to "string". I got that from the page cited in my last reply. Which is a very specific page for strings and missing values.