How to extract table data using function variable?

I have a function pulling data from tables stored in a cell array, and it depends on which column's data I want. In this case, the two variables are 'Dose' and 'Volume'.

Instead of indexing by '.VariableName' in two functions, I can use only one function with a switch block to extract data using parenthetical integers.

How do I extract data directly using the VarN (VariableName) string directly as the index variable name? MATLAB objects that the string variable is not the table variable:

>> newvoldata{5}.test{1}(1:2,:)
Unrecognized variable name 'test'.
>> test{1}

 ans =

    'Dose'

Here is the function I'm looking to simplify by removing the switch block and changing the table indexing method:

function output = GetDataFromEachCell(cellarray,string,VarN)
% decide which variable to pull
switch VarN
    case 'dose'
        VarInt = 4;
    case 'vol'
        VarInt = 5;
    otherwise
        error('Specify either ''dose'' or ''vol''!')
end
% count the number of cell elements
 counter = 0;
 for loop = 1:length(cellarray)
    counter = counter + size(cellarray{loop},1);
 end
% loop through each cell 
 output = zeros(1,counter);
 bookmark = 1;
 for loop = 1:length(cellarray)
     if ~isempty(cellarray{loop})
       output(bookmark:bookmark+length(cellarray{loop}(strcmpi(cellarray{loop}.DistributionType,string),:).(VarInt))-1) =...
                                       cellarray{loop}(strcmpi(cellarray{loop}.DistributionType,string),:).(VarInt);
          bookmark = bookmark + length(cellarray{loop}(strcmpi(cellarray{loop}.DistributionType,string),:).(VarInt));
     end
 end
end

Answer 1

[Peter Perkins]

Daniel, I'm not exactly sure what you are asking, but i think the following might help. All of these kinds of "dot subscripting" are equivalent:

>> t = array2table(rand(2))
t =
  2×2 table
     Var1        Var2  
    _______    ________
    0.74815    0.083821
    0.45054     0.22898
>> t.Var1
ans =
      0.74815
      0.45054
>> t.('Var1'); % noone would ever actually do this
>> vname = 'Var1'; t.(vname);
>> t.(1);

[Stephen23]

See also the MATLAB documentation:

https://www.mathworks.com/help/matlab/matlab_prog/access-data-in-a-table.html

[Daniel Bridges]

Why do you say 'no one would ever actually do this'? What is wrong with that method? Specifically, is there a better way than the following code (i.e. passing the variable name into a function to access table data)?

Doses.Planned = GetDataFromEachCell(newvoldata,'planned',SelectedPatients,'Dose');
Doses.Blurred = GetDataFromEachCell(newvoldata,'blurred',SelectedPatients,'Dose');
Vols.Planned = GetDataFromEachCell(newvoldata,'planned',SelectedPatients,'Volume');
Vols.Blurred = GetDataFromEachCell(newvoldata,'blurred',SelectedPatients,'Volume');

function output = GetDataFromEachCell(cellarray,string,SelectedStudyID,VarN)
% count the number of cell elements
 counter = 0;
 for loop = 1:length(cellarray)
    counter = counter + size(cellarray{loop},1);
 end
% loop through each cell 
 output = zeros(1,counter);
 bookmark = 1;
 for loop = 1:length(cellarray)
     if ~isempty(cellarray{loop})
         for PtLoop = SelectedStudyID
       output(bookmark:bookmark+length(...
      cellarray{loop}(strcmpi(cellarray{loop}.DistributionType,string) & cellarray{loop}.StudyID==PtLoop,:).(VarN))...
                                      -1) = ...
      cellarray{loop}(strcmpi(cellarray{loop}.DistributionType,string) & cellarray{loop}.StudyID==PtLoop,:).(VarN);

            bookmark = bookmark + length(...
        cellarray{loop}(strcmpi(cellarray{loop}.DistributionType,string) & cellarray{loop}.StudyID==PtLoop,:).(VarN));
           end
       end
   end
  end

Stephen, that page does not clearly say that vname = 'Var1'; t.(vname) works. Rather, it suggests one would execute vname = 'Var1'; t.vname.