MATLAB: How to bypass empty fields in structure when loading data

merge

My experiment contains my subjects data and each subject consists of different blocks before I do the analysis I merged my data into one mat file, but some of my subjects have missing blocks, so I bypassed those data and merge the file. However the problem is missing blocks represent like this [ ], since some blocks are like this [ ], when I want to load different field of my structure I get this error '' Dot indexing is not supported for variables of this type '' Therefore I need to bypass these blocks in the loop, In this regard I added this code 
 if isempty(all_Subjects(block_Counter, subject_Counter).all_results) == 0
     % do the workk
 else
     break
 end
but I got empty results for saving my data in table
% merging Information of different Subjects

Subjects_ID = [];
Blocks_ID = [];
reactionTime_of_all_Subjects = [];
performance_of_all_Subjects = [];
for subject_Counter = s_Initial:s_Final
    
    % select data with fields
 if isempty(all_Subjects(block_Counter, subject_Counter).all_results) == 0
    
    % merging Information of different blocks

    all_reactionTime_of_one_Subject = [];
    all_subject_Performance_of_one_Subject = [];
    
    for block_Counter =  B_Initial:B_Final
        
        reactionTime =  all_Subjects(block_Counter, subject_Counter).all_results.reactionTime;
        subject_Performance =  all_Subjects(block_Counter, subject_Counter).all_results.performance;
        
         % merging Information of different blocks
        all_reactionTime_of_one_Subject = [all_reactionTime_of_one_Subject; reactionTime];
        all_subject_Performance_of_one_Subject = [all_subject_Performance_of_one_Subject; subject_Performance];
        
        % Generate label for Subjects
        for i = 1: length(reactionTime)
            
            Subjects_ID = [Subjects_ID; subject_Counter]
            Blocks_ID = [Blocks_ID; block_Counter]
        end
    end
    
    % merging Information of different Subjects
    performance_of_all_Subjects = [performance_of_all_Subjects; all_subject_Performance_of_one_Subject];
    reactionTime_of_all_Subjects = [reactionTime_of_all_Subjects; all_reactionTime_of_one_Subject];
     else
        break
end
   
end
% Mering all data to table
analysis = array2table([Subjects_ID, Blocks_ID, reactionTime_of_all_Subjects, performance_of_all_Subjects]);
analysis.Properties.VariableNames{1} = 'Subjects_ID';
analysis.Properties.VariableNames{2} = 'Block_ID';
analysis.Properties.VariableNames{3} = 'ReactionTime';
analysis.Properties.VariableNames{4} = 'Performance';
save('data_for_Analysis','analysis')

Best Answer

Use isstruct(): https://www.mathworks.com/help/releases/R2020a/matlab/ref/isstruct.html. For example, use the following if condition to only access data of it is a struct
if isstruct(all_Subjects(block_Counter, subject_Counter).all_results)
    reactionTime =  all_Subjects(block_Counter, subject_Counter).all_results.reactionTime;
    subject_Performance =  all_Subjects(block_Counter, subject_Counter).all_results.performance;
else
    reactionTime =  0; % or something else
    subject_Performance = 0;
end
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