How to extract table data using function variable?

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Daniel Bridges
Daniel Bridges 2018-3-7
编辑： Daniel Bridges 2018-3-9
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

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回答（1 个）

Peter Perkins
Peter Perkins 2018-3-8
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);
  2 个评论
Daniel Bridges
Daniel Bridges 2018-3-9
编辑：Daniel Bridges 2018-3-9
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.

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