Consider the following matrix:
a=[1,2,3]
therefore
size(a)=[1,3]
I want to assign the second dimension 3 to variable n. What is the most efficient way?
Why are the following not working?
[[],n]=size(a)
or
n= num2cell(size(a)){2}
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Seems like the most neat way is to use a temporary variable. stackoverflow.com/questions/3627107/…godblessfq– godblessfq2013-08-15 23:04:03 +00:00Commented Aug 15, 2013 at 23:04
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1 Answer
This is probably the simplest, and works for a with any number of dimensions:
n = size(a,2);
If a is guaranteed to have exactly 2 dimensions, you could also use
[ m, n ] = size(a);
and if you don't need the first variable, in recent versions of Matlab you can write
[ ~, n ] = size(a);
As for the things you have tried:
[[],n]=size(a)does not work because[]is not a variable to which you can assign anything.n= num2cell(size(a)){2}does not work because you can't directly index like that in Matlab. You would need a temporary variable:temp = num2cell(size(a)); n=temp{2}. Or dispose ofnum2celland do:temp = size(a); n=temp(2).
3 Comments
Amro
The first code is the correct one. Careful about the others,
size will return the product of the remaining dimensions if you dont specify enough output variables; example: x = rand(5,4,3,2); [~,n] = size(x); (n will be equal to 4*3*2)Amro
if you dont know the number of dimensions, another way is to do:
[~,n,~] = size(x) this will work even if ndims(x)==2. Of course size(x,2) is the still the preferred way.
JustinBlaber
Also,
~ doesn't work for older versions of matlab. Specifically R2009a on my laptop, not sure about other revisions.