Convert Json cells/struct to table

Question

Dion Theunissen 2022-5-10

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1715690-convert-json-cells-struct-to-table

回答： Ravi 2023-10-5

I have an API request and want to convert in in a table.

The response is a cell build out of structs. Every row in de cell needs to be a row in the table. The structs are build out of charts, doubles and structs again. Now i made the following but it looks like this is not the right and quickest way. I fill the RawDataAPI (empty table) by getting every value one by one.

for i2 = 1:size(response3)
    RawDataAPI.triggerType(i2) = string(response3{i2, 1}.triggerType);
    RawDataAPI.vehicleIdentificationNumber(i2) = string(response3{i2, 1}.vehicleIdentificationNumber);
    RawDataAPI.UniekId(i2) = string(response3{i2, 1}.driverIdentification);
    RawDataAPI.createdTimestamp(i2) = string(response3{i2, 1}.createdTimestamp);
    RawDataAPI.receivedTimestamp(i2) = string(response3{i2, 1}.receivedTimestamp);
    RawDataAPI.distance(i2) = (response3{i2, 1}.distance);
    RawDataAPI.distanceCruiseControl(i2) = (response3{i2, 1}.distanceCruiseControl);
    RawDataAPI.weight(i2) = (response3{i2, 1}.weight);
    RawDataAPI.fuelUsed(i2) = (response3{i2, 1}.fuelUsed);
    RawDataAPI.fuelUsedSpeedZero(i2) = (response3{i2, 1}.fuelUsedSpeedZero);
    RawDataAPI.fuelUsedPto(i2) = (response3{i2, 1}.fuelUsedPto);
    RawDataAPI.durationUsedPto(i2) = (response3{i2, 1}.durationPto);
    RawDataAPI.durationSpeedOverZero(i2) = (response3{i2, 1}.durationSpeedOverZero);
    RawDataAPI.durationSpeedZero(i2) = (response3{i2, 1}.durationSpeedZero);
    RawDataAPI.distanceCoasting(i2) = (response3{i2, 1}.distanceCoasting);
    RawDataAPI.durationCruiseControl(i2) = (response3{i2, 1}.durationCruiseControl);
    RawDataAPI.brakeCounter(i2) = (response3{i2, 1}.brakeCounter);
    RawDataAPI.latitude(i2) = (response3{i2, 1}.latitude);
    RawDataAPI.longitude(i2) = (response3{i2, 1}.longitude);
    RawDataAPI.altitude(i2) = (response3{i2, 1}.altitude);
    RawDataAPI.Acc03(i2) =  [response3{i2, 1}.acceleration(1).value].';
    RawDataAPI.Acc05(i2) =  [response3{i2, 1}.acceleration(2).value].';
    RawDataAPI.Acc07(i2) =  [response3{i2, 1}.acceleration(3).value].';
    RawDataAPI.Acc09(i2) =  [response3{i2, 1}.acceleration(4).value].';
    RawDataAPI.Acc11(i2) =  [response3{i2, 1}.acceleration(5).value].';
    RawDataAPI.Acc15(i2) =  [response3{i2, 1}.acceleration(6).value].';
    RawDataAPI.Acc2(i2) =  [response3{i2, 1}.acceleration(7).value].';
    RawDataAPI.Acc25(i2) =  [response3{i2, 1}.acceleration(8).value].';
    RawDataAPI.Acc3(i2) =  [response3{i2, 1}.acceleration(9).value].';
    RawDataAPI.Acc35(i2) =  [response3{i2, 1}.acceleration(10).value].';
    RawDataAPI.Acc4(i2) =  [response3{i2, 1}.acceleration(11).value].';
    RawDataAPI.Brake03(i2) =  [response3{i2, 1}.brake(1).value].';
    RawDataAPI.Brake05(i2) =  [response3{i2, 1}.brake(2).value].';
    RawDataAPI.Brake07(i2) =  [response3{i2, 1}.brake(3).value].';
    RawDataAPI.Brake09(i2) =  [response3{i2, 1}.brake(4).value].';
    RawDataAPI.Brake11(i2) =  [response3{i2, 1}.brake(5).value].';
    RawDataAPI.Brake15(i2) =  [response3{i2, 1}.brake(6).value].';
    RawDataAPI.Brake2(i2) =  [response3{i2, 1}.brake(7).value].';
    RawDataAPI.Brake25(i2) =  [response3{i2, 1}.brake(8).value].';
    RawDataAPI.Brake3(i2) =  [response3{i2, 1}.brake(9).value].';
    RawDataAPI.Brake35(i2) =  [response3{i2, 1}.brake(10).value].';
    RawDataAPI.Brake4(i2) =  [response3{i2, 1}.brake(11).value].';
 
    RawDataAPI.Torque1(i2) =  [response3{i2, 1}.torque(1).value].';
    RawDataAPI.Torque2(i2) =  [response3{i2, 1}.torque(2).value].';
    RawDataAPI.Torque3(i2) =  [response3{i2, 1}.torque(3).value].';
    RawDataAPI.Torque4(i2) =  [response3{i2, 1}.torque(4).value].';
    RawDataAPI.Torque5(i2) =  [response3{i2, 1}.torque(5).value].';
    RawDataAPI.Torque6(i2) =  [response3{i2, 1}.torque(6).value].';
    RawDataAPI.Torque7(i2) =  [response3{i2, 1}.torque(7).value].';
    RawDataAPI.Torque8(i2) =  [response3{i2, 1}.torque(8).value].';
    RawDataAPI.Torque9(i2) =  [response3{i2, 1}.torque(9).value].';
    RawDataAPI.Torque10(i2) =  [response3{i2, 1}.torque(10).value].';
    RawDataAPI.Speed1(i2) =  [response3{i2, 1}.speed(1).value].';
    RawDataAPI.Speed2(i2) =  [response3{i2, 1}.speed(2).value].';
    RawDataAPI.Speed3(i2) =  [response3{i2, 1}.speed(3).value].';
    RawDataAPI.Speed4(i2) =  [response3{i2, 1}.speed(4).value].';
end

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Answer 1

Ravi 2023-10-5

0
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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1715690-convert-json-cells-struct-to-table#answer_1326284

在 MATLAB Online 中打开

Hi Dion Theunissen,

According to my understanding, you want to shorten your code avoiding writing redundant statements.

You can use the “eval” function for this purpose. This can be broken down into few steps.

Find the properties that are present in the struct using “fieldnames” function and store them in an array.
Since, now you have the field names. You can access the field by writing an expression in the eval function.

myCourse = struct("coursename", "MATLAB", "number_of_students", 100, "duration", "6 weeks"); 
required = 'duration'; 
ans = eval(['myCourse.', char(required)]); 
disp(ans); 

The eval function here evaulates the expression, “myCourse.duration” and stores that answer in “ans” variable.

Loop over the field names and assign them to the corresponding table variable name.

%   triggerType 
var = 'triggerType'; 
eval(["RawDataAPI.", char(var), "(i) = string(response3(", num2str(i), ".", char(var)]); 
%   torque 
for j=1:10 
    eval(["RawDataAPI.Torque", num2str(j), "(", num2str(i), ") = [response3{", num2str(i), ", 1}.torque(", num2str(j), ").value"]); 
end 

Though this helps you shorten your code a bit, yet there are some statements that you need to write manually because there is no pattern in the variable names of the table, for example “Acc”, “Brake”.

For more understanding about the “eval” function kindly refer to the below provided links.