Create excel file from json variable value

I think there is an easy solution to this but I keep running into the same issue.

I want to create an excel file from a json value. The json file is stored in subject-specific folders (all with the same general path).

All json variables appear at the same line in the json file

My current code:

clear
subjs = {'SUB2114'
         'SUB2116'
         'SUB2118'};
subjs=subjs.';

for i=1:length(subjs)
    
    %cd to folder with json files
    cd (['/Volumes/myDirectory/' subjs{i} '/folder/']);
    %read AP json file
    jsonText = fileread('Fieldmapap.json');
    jsonData = jsondecode(jsonText);
    ap = jsonData.PhaseEncodingDirection;
    ap=ap.';
    % write json (not needed?)
    encodedJSON = jsonencode(ap);
    jsonText2 = jsonencode(jsonData);
    fid = fopen('J_script_test.json', 'w');
    fprintf(fid, encodedJSON);
    fclose(fid);
    
end %subject loop

%write table with subjects in first column and encodedJSON value in second column
T=cell2table([subjs encodedJSON]);
writetable(T,'Tester.csv');

I have also tried the mytable function (below) with no positive results.

mytable=table('Size',[3 2],'VariableTypes',{'cellstr';'cellstr'},'VariableNames',{'subjects';'direction'});
mytable{i,'subjects'} = {subjs};
mytable{i,'direction'} = {ap};

I keep getting an output that lists subjects horizontally with the last subjects direction value.

I think I am missing something simple (like, i+1 function), but do not know!

Any help would be appreciated!

[Rik]

Your loop is overwriting the results, and it would seem that your alternative would also be placed inside the loop, causing the variable to be recreated every iteration.

What is it exactly you want to achieve? Do you want a cell array with the subject ID in one column and the phase encoding in the second column?

[Nikki]

That is correct, I want a cell array/table with the subject ID in one column and phase encoding in the second column.

Answer 1

[Voss]

It's difficult to say for sure without one of your json files to test with, but something like this might work:

subjs = {'SUB2114'
         'SUB2116'
         'SUB2118'};

Nsubjs = numel(subjs);

directions = cell(Nsubjs,1);

for ii = 1:Nsubjs
    
    filename = fullfile('Volumes','myDirectory',subjs{ii},'folder','Fieldmapap.json');
    
    jsonData = jsondecode(fileread(filename));
    
    directions{ii} = char(jsonData.PhaseEncodingDirection);
    
end

T = table(subjs,directions,'VariableNames',{'subjects','direction'});

writetable(T,'Tester.csv');

Avoid using cd. Instead, construct the absolute or relative path to the file, as shown above using fullfile.

Answer 2

[Eric Sofen]

I'm roughing this a bit since I don't have your JSON data files, but the below approach puts your file names in a table, then uses rowfun to iterate over the table, reading the corresponding JSON file and returning the corresponding phase encoding.

subjs = {'SUB2114'
         'SUB2116'
         'SUB2118'};
t = table(subjs);
ph = rowfun(@getPhaseEncodingDirection,t,InputVariables="subjs",OutputVariableNames="PhaseEncodingDirection");
t = [t ph]

function ap = getPhaseEncodingDirection(subj)
    %read AP json file
    jsonText = fileread("/Volumes/myDirectory/" + subj + "/folder/Fieldmapap.json");
    jsonData = jsondecode(jsonText);
    ap = jsonData.PhaseEncodingDirection;
end

Answer 3

[Nikki]

Thank you both! Both edits worked but @Voss 's code outputted into a .csv, which will be easier to check (I have way more subjects than what is listed).

Very new to MATLAB coding so thanks for the help @Voss @Eric Sofen !