Sort JSON by values in MATLAB

Question

I would like to sort my values in the JSON file order by "createdAt" and use these values in the plot function. As you can see this column stores date value so I've converted it. And I've applied the sort function but when I see the output of the data, it seems sort does not apply.

data = loadjson('C:/data/default.json');
count_data = sum(cellfun(@(x) numel(x),data.Location)); %returns 21

for i=1:count_data
   createdAt= cellfun( @(cellElem) cellElem.createdAt, data.Location ,'UniformOutput',false);
   createdAtDate= datetime(createdAt(i),'InputFormat','dd-MM-yyyy HH:mm:ss','Format', 'dd-MM-yyyy n HH:mm:ss');
    [~,X] = sort(createdAtDate,'descend');
    out=data(X);
end

for i=1:count_data
  x = cellfun( @(cellElem) cellElem.createdAt, out.Location,'UniformOutput',false);
  disp(x);
 end

My JSON file:

"Location": [
{
  "id": "0b5965e5-c509-4522-a525-8ef5a49dadaf",
  "measureId": "5a6e9b79-dbb1-4482-acc1-d538f68ef01f",
  "locationX": 0.9039769252518151,
  "locationY": 0.2640594070404616,
  "createdAt": "06-01-2021 19:38:44"
},
{
  "id": "18714a2f-a8b3-4dc6-8a5b-114497fa9671",
  "measureId": "671f52bc-a066-494a-9dce-6e9ccfac6c1d",
  "locationX": 1.5592001730078755,
  "locationY": 0.5207689756815629,
  "createdAt": "06-01-2021 19:35:24"
},

Thanks in advance.

Answer 1

You need to extract all of the data you need, then sort

i.e.

x = cellfun( @(cellElem) cellElem.locationX, data.Location );
y = cellfun( @(cellElem) cellElem.locationY, data.Location );
% Get date strings
d = cellfun( @(cellElem) cellElem.createdAt, data.Location, 'UniformOutput', false)
% Convert to datetime
d = datetime( d, 'InputFormat', 'dd-MM-yyyy HH:mm:ss' );
% Get the sort order
[~,idx] = sort( d );
% Sort other arrays
x = x(idx);
y = y(idx);

Another option would be to use tables

x = cellfun( @(cellElem) cellElem.locationX, data.Location );
y = cellfun( @(cellElem) cellElem.locationY, data.Location );
% Get dates
d = cellfun( @(cellElem) cellElem.createdAt, data.Location, 'UniformOutput', false)
d = datetime( d, 'InputFormat', 'dd-MM-yyyy HH:mm:ss' );
% Create table
t = table( x(:), y(:), d(:), 'VariableNames', {'locationX','locationY','createdAt'} );
% Sortrows
t = sortrows( t, 'createdAt' );

You have to use a table rather than a matrix here (although sortrows can accept either) because of the mixed data types across the columns.