MATLAB Answers


Matlab "missing" values not clear

Asked by Temitope Akinpelu on 23 Mar 2017
Latest activity Answered by Jan
on 23 Mar 2017
Matlab holds some types of "<missing>" values in its string array. For instance
b =
3×3 string array
"I" <missing> "MATLAB"
<missing> "love" "MATLAB"
"I" "love" <missing>
when I access each element of the array
ans =
ans =
ans =
errormsg = Conversion of element 2 from missing to character vector is not supported.
what type of value is "missing", and why can't it simply be an empty character vector?


@Temitope Akinpelu: how did you create the variable b ?

Sign in to comment.



2 Answers

Answer by Guillaume
on 23 Mar 2017
Edited by Guillaume
on 23 Mar 2017
 Accepted Answer

what type of value is "missing"
From the user point of view it's a flag for missing data. How it is implemented should not concern you and is not documented. (And I don't mean that in a negative way. We, as users, should not have to care, it should 'just work')
and why can't it simply be an empty character vector I don't know if it's a deliberate decision from mathworks or an oversight. However, there are plenty of cases where a missing string is not the same at all as an empty string.
Note that missing is brand new as of R2017a. As is documented the curly braces syntax is a compatibility layer for these codes that rely on cell array of char arrays and you should try to avoid it. It is indeed a bit unfortunate that that compatibility layer breaks in case of missing, so if you want that changed create a bug report with mathworks.


Sign in to comment.

Answer by Jan
on 23 Mar 2017

"Missing" means, that the string was not defined before. An empty string would be a defined string already. This is something completely different.
With cell arrays an equivalent method was implemented for cell arrays, but not visible from the Matlab layer:
C = cell(1, 5)
Now the contents of C{1} is treated as empty matrix [], but internally the element contains a NULL pointer. From the MEX level this must be considered explicitely - with the advantage that it can be distinguished also.


Sign in to comment.