MATLAB: Replace a missing string in a table

Question

I want to replace all missing strings in a table with a string of my choice, say 'unknown'. I use R2016a (without an upgrade option), so functions like fillmissing are not available to me, in case they could be of help. Eg:

 dblVar = [NaN; 3; 7; 9];
 cellstrVar = {'one'; 'three'; ''; 'nine'};
 categoryVar = categorical({''; 'red'; 'yellow'; 'blue'});
 A = table(dblVar, cellstrVar, categoryVar)
A = 
    dblVar    cellstrVar    categoryVar
    ______    __________    ___________
    NaN       'one'         <undefined>
      3       'three'       red        
      7       ''            yellow     
      9       'nine'        blue

I would like to end up with this:

 A = 
    dblVar    cellstrVar    categoryVar
    ______    __________    ___________
    NaN       'one'         unknown
      3       'three'       red        
      7       'unknown'     yellow     
      9       'nine'        blue

Note I also replaced the categorical '<undefined>' as well, if you can please include in your answer.

Is there a way to do this without changing A's structure, eg from table to cell, in the process? The reason I want to avoid the transformation is my table is large, and transformation may cause memory issues.

Edit to add: the location of the missing string value has to be identified as well, there may be several such columns in the table.

Many thanks.

Answer 1

This should work:

dblVar = [NaN; 3; 7; 9];
cellstrVar = {'one'; 'three'; ''; 'nine'};
categoryVar = categorical({''; 'red'; 'yellow'; 'blue'});
cellstrVar2 = {'four'; 'none'; '7'; ''};
A = table(dblVar, cellstrVar, categoryVar, cellstrVar2);
varNames = A.Properties.VariableNames;
for ii = 1:numel(varNames)
     if iscellstr(A{1,varNames{ii}})
         undefloc = strcmp(A.(ii), '');
         A{undefloc, ii} = cellstr('unknown');
     end
     if iscategorical(A{1, varNames{ii}})
         undefloc = isundefined(A{:,ii});
         A{undefloc, ii} = categorical(cellstr('unknown'));
     end
end
A = 
    dblVar    cellstrVar    categoryVar    cellstrVar2
    ______    __________    ___________    ___________
    NaN       'one'         unknown        'four'     
      3       'three'       red            'none'     
      7       'unknown'     yellow         '7'        
      9       'nine'        blue           'unknown'

You can use the undefloc variable to find where things were undefined or empty strings.