How to specify input arguments of a structure in a 'for' loop separate to field argument

Hi,

I am using MATLAB R2020a on a MacBook Air. I am trying to record the results of an experiment such that the results are inserted after each trial. This involves placing the field argument of the structure separate to the input arguments for the structure in a for loop iterating from 1 to 'n' number of trials like this (I have only included some of the input arguments for simplicity):

resultsMatrix = struct('TrialOrder', {}, 'TrialType', {}, 'S1Numbers', {}, 'S1Mean', {}, 'S1Variance', {}, 'S1Position', {}, 'S2Number', {}, 'S2Numbers', {}, 'S2Mean', {}, 'S2Variance', {}, 'S2Position', 'S3Number', {}, 'S3Numbers', {}, 'S3Mean', {}, 'S3Variance', {}, 'S3Position', {}, 'Key1', {},  'Timeq1', {}, 'Srightnumber', {}, 'Srightnumbers', {}, 'Srightmean', {}, 'Srightvariance', {}, 'Sleftnumber', {}, 'Sleftnumbers', {}, 'Sleftmean', {}, 'Sleftvariance', {}, 'Key2', {},  'Timeq2', {});

for i = 1:nTrials
    resultsMatrix(i).TrialOrder = 1;
    resultsMatrix(i).TrialType = randtemp(1);
    resultsMatrix(i).S1Numbers = num2str(seq1);
    resultsMatrix(i).S1Mean = 10;
    resultsMatrix(i).S1Variance = 20;
    resultsMatrix(i).S1Position = randpos{1};
    resultsMatrix(i).S2Numbers = num2str(seq2);
end

However, I keep getting the following error:

Error using struct
Field and value input arguments must come in pairs.

Error in Fourth_draft (line 147)
resultsMatrix = struct('TrialOrder', {}, 'TrialType', {}, 'S1Numbers', {}, 'S1Mean', {}, 'S1Variance', {},
'S1Position', {}, 'S2Number', {}, 'S2Numbers', {}, 'S2Mean', {}, 'S2Variance', {}, 'S2Position', 'S3Number',
{}, 'S3Numbers', {}, 'S3Mean', {}, 'S3Variance', {}, 'S3Position', {}, 'Key1', {},  'Timeq1', {},
'Srightnumber', {}, 'Srightnumbers', {}, 'Srightmean', {}, 'Srightvariance', {}, 'Sleftnumber', {},
'Sleftnumbers', {}, 'Sleftmean', {}, 'Sleftvariance', {}, 'Key2', {},  'Timeq2', {});

I would very much appreciate if somebody could help me with this, thank you!

Answer 1

[Adam Danz]

This is why long lines of code should be broken up into separate lines.

resultsMatrix = struct('TrialOrder', {}, 'TrialType', {}, 'S1Numbers', {}, 'S1Mean', {}, ...
    'S1Variance', {}, 'S1Position', {}, 'S2Number', {}, 'S2Numbers', {}, 'S2Mean', {}, ...
    'S2Variance', {}, 'S2Position', 'S3Number', {}, 'S3Numbers', {}, 'S3Mean', {}, 'S3Variance',{}, ...
    'S3Position', {}, 'Key1', {},  'Timeq1', {}, 'Srightnumber', {}, 'Srightnumbers', {}, ...
    'Srightmean', {}, 'Srightvariance', {}, 'Sleftnumber', {}, 'Sleftnumbers', {}, 'Sleftmean', {}, ...
    'Sleftvariance', {}, 'Key2', {},  'Timeq2', {});

Hint: One of your fields is missing a {} (3rd row).

[Cai Chin]

Ah yes, thank you so much - I shall bear that in mind in the future.

[Stephen23]

Rather than writing out {} a thousand times, just use some indexing and a comma-separated list:

C = {'TrialOrder', 'TrialType', 'S1Numbers', 'S1Mean', ...};
C(2,:) = {{}};
S = struct(C{:});

https://www.mathworks.com/help/matlab/matlab_prog/comma-separated-lists.html

https://www.mathworks.com/matlabcentral/answers/320713-how-to-operate-on-comma-separated-lists

[Cai Chin]

Thank you for this suggestion

Answer 2

[meghannmarie]

You are missing {} after 'S2Position'

resultsMatrix = struct('TrialOrder', {},... , 'S2Variance', {}, 'S2Position', 'S3Number', {}, 'S3Numbers', {},...

[Cai Chin]

Thank you very much!