# How to get the "zero/blank" element of a given variable?

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royk am 29 Aug. 2019
Kommentiert: royk am 30 Aug. 2019
I have an array VAR of unknown type. When the array is extended, Matlab knowns how to fill in blank ("zero") values of the correct type. How do I get this default blank value for any given Var type?
One solution is simply to extend an array and see what value gets padded:
BLANK(2) = VAR(1) ; BLANK(2) = [] ;
This returns a scalar BLANK with the correct "0" value and works for any VAR type.
BUT: It doesn't work with empty VAR.
Any thoughts of a general way to get the Blank value for any given array even if empty?
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### Akzeptierte Antwort

Rik am 29 Aug. 2019
Bearbeitet: Rik am 29 Aug. 2019
You can abuse repmat for this:
a=uint8(8);
repmat(a,0,0)
b='foo_bar';
repmat(b,0,0)
Edit:
a=uint8(8);b='foo_bar';c={'1',2};
get_blank_val=@(x) eval([class(x) '(0)']);
get_blank_val(a)
get_blank_val(b)
get_blank_val(c)
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Rik am 29 Aug. 2019
You could put in a special condition for a struct, but then you can't make it an anonymous function anymore.
function blank=get_blank_val(x)
if ~isa(x,'struct')
blank=eval([class(x) '(0)']);
else
fn=fieldnames(x);
tmp=[fn repmat({[]},size(fn))]';
blank=struct(tmp{:});
end
end
royk am 30 Aug. 2019
that will do the job
there are still other exceptions. for example, for an array of MyClass objects, Matlab determines Blank for array extension by calling empty(MyClass).
It thereby feels like there got to be a generic Matlab function that returns the Blank object for array extension for ANY type.
Anyway, your kind suggestion above surely does the job for my needs.
thanks!

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