在 MATLAB 中按值排序 JSON

Question

我想按“createdAt”对 JSON 文件中的值进行排序，并在绘图函数中使用这些值。如您所见，此列存储日期值，因此我已将其转换。我已经应用了排序功能，但是当我看到数据的输出时，似乎排序不适用。

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

我的 JSON 文件：

"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"
},

提前致谢。

Answer 1

您需要提取所有需要的数据，然后排序

即

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);

另一种选择是使用 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' );

您必须在此处使用 table 而不是矩阵（尽管 sortrows 可以接受任何一种），因为列中的数据类型混合。

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