How can I read a .json file?

Question

Carlyle Hickman 2017-2-24

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/326764-how-can-i-read-a-json-file

编辑： cui,xingxing 2024-4-27，2:04

Hello I found some data on the web that requires me to open a .gz file and a .json. I was able to unzip the gz file in MATLAB but have not been able to read the .json.

My Code:

>> fname = 'meta_Electronics.json';
>> fid = fopen(fname);
>> raw = fread(fid,inf);
>> str = char(raw');
>> fclose(fid);
>> data = JSON.parse(str)

and this is the error that is displayed:

Undefined variable "JSON" or class "JSON.parse".

Can someone point me in the right direction, as far as what i need to change?

Cheers.

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Adam 2017-2-24

在 MATLAB Online 中打开

I looked on the File Exchange when I wanted to read a json file, then downloaded something from there and made various edits to it to speed it up a bit. There are a few submissions on there that will read json files.

If you haven't defined anything called JSON though then

data = JSON.parse(str);

is highly optimistic coding. It's a very good way to code from the top level down using idealised code, but only if you write the code that you are calling too rather than just assume it will appear somehow!

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Answer 1

Alka Nair 2017-11-22

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/326764-how-can-i-read-a-json-file#answer_292588

在 MATLAB Online 中打开

 fname = 'meta_Electronics.json'; 
fid = fopen(fname); 
raw = fread(fid,inf); 
str = char(raw'); 
fclose(fid); 
val = jsondecode(str);

worked for me.

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Tolga Karabiyikoglu 2020-11-12

Cool- seems to work for me too

Juan Miguel Serrano Rodríguez 2021-10-19

Thanks!

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Answer 2

Elbi Mutluoglu 2020-2-13

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/326764-how-can-i-read-a-json-file#answer_415430

How can I read this json file as array.

{"flowSegmentData":{"frc":"FRC0","currentSpeed":30,"freeFlowSpeed":85,"currentTravelTime":28,"freeFlowTravelTime":10,"confidence":0.9900000095367432,"roadClosure":false,"coordinates":{"coordinate":[{"latitude":40.99520713231141,"longitude":29.11316083692566},{"latitude":40.9951128720138,"longitude":29.11348934584032},{"latitude":40.99499782625885,"longitude":29.113922597143414},{"latitude":40.99492447823734,"longitude":29.11425589372996},{"latitude":40.99481265425299,"longitude":29.114754874308034},{"latitude":40.9947156413892,"longitude":29.115239700057685},{"latitude":40.99469244741794,"longitude":29.115362205564793},{"latitude":40.99466308297875,"longitude":29.115527466260318},{"latitude":40.99465731538117,"longitude":29.11556668313179},{"latitude":40.99465324816397,"longitude":29.115588820406316},{"latitude":40.9946365659001,"longitude":29.115684510886638},{"latitude":40.994617484549394,"longitude":29.11581043877149},{"latitude":40.99460761712758,"longitude":29.115881261564937}]},"@version":"traffic-service 3.2.001"}}

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Nitesh Panchal 2021-4-26

编辑：Nitesh Panchal 2021-4-26

please use----- {jsondecode('[ ----------------please paste your json code here------------- ]')}

{jsondecode('[{"flowSegmentData":{"frc":"FRC0","currentSpeed":30,"freeFlowSpeed":85,"currentTravelTime":28,"freeFlowTravelTime":10,"confidence":0.9900000095367432,"roadClosure":false,"coordinates":{"coordinate":[{"latitude":40.99520713231141,"longitude":29.11316083692566},{"latitude":40.9951128720138,"longitude":29.11348934584032},{"latitude":40.99499782625885,"longitude":29.113922597143414},{"latitude":40.99492447823734,"longitude":29.11425589372996},{"latitude":40.99481265425299,"longitude":29.114754874308034},{"latitude":40.9947156413892,"longitude":29.115239700057685},{"latitude":40.99469244741794,"longitude":29.115362205564793},{"latitude":40.99466308297875,"longitude":29.115527466260318},{"latitude":40.99465731538117,"longitude":29.11556668313179},{"latitude":40.99465324816397,"longitude":29.115588820406316},{"latitude":40.9946365659001,"longitude":29.115684510886638},{"latitude":40.994617484549394,"longitude":29.11581043877149},{"latitude":40.99460761712758,"longitude":29.115881261564937}]},"@version":"traffic-service 3.2.001"}}]')}

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Answer 3

cui,xingxing 2023-8-14

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/326764-how-can-i-read-a-json-file#answer_1287117

编辑：cui,xingxing 2024-4-27，2:04

在 MATLAB Online 中打开

test.zip

My personal opinion is that there is still no direct mapping from a generic readable json file to MATLAB's built-in types (struct or dictionary). The readstruct function is expected to support more file formats.

But on the other hand, you don't really need to call low-level functions such as fread, you can just use the fileread function to read the content and then decode it. For example, the following operation:

!unzip test.zip # see attachment file,use @Elbi Mutluoglu data for example
Archive:  test.zip
  inflating: test.json               

View json file contents, preview it.

!cat test.json
{
    "flowSegmentData": {
        "frc": "FRC0",
        "currentSpeed": 30,
        "freeFlowSpeed": 85,
        "currentTravelTime": 28,
        "freeFlowTravelTime": 10,
        "confidence": 0.9900000095367432,
        "roadClosure": false,
        "coordinates": {
            "coordinate": [
                {
                    "latitude": 40.99520713231141,
                    "longitude": 29.11316083692566
                },
                {
                    "latitude": 40.9951128720138,
                    "longitude": 29.11348934584032
                },
                {
                    "latitude": 40.99499782625885,
                    "longitude": 29.113922597143414
                },
                {
                    "latitude": 40.99492447823734,
                    "longitude": 29.11425589372996
                },
                {
                    "latitude": 40.99481265425299,
                    "longitude": 29.114754874308034
                },
                {
                    "latitude": 40.9947156413892,
                    "longitude": 29.115239700057685
                },
                {
                    "latitude": 40.99469244741794,
                    "longitude": 29.115362205564793
                },
                {
                    "latitude": 40.99466308297875,
                    "longitude": 29.115527466260318
                },
                {
                    "latitude": 40.99465731538117,
                    "longitude": 29.11556668313179
                },
                {
                    "latitude": 40.99465324816397,
                    "longitude": 29.115588820406316
                },
                {
                    "latitude": 40.9946365659001,
                    "longitude": 29.115684510886638
                },
                {
                    "latitude": 40.994617484549394,
                    "longitude": 29.11581043877149
                },
                {
                    "latitude": 40.99460761712758,
                    "longitude": 29.115881261564937
                }
            ]
        },
        "@version": "traffic-service 3.2.001"
    }
}
myJsonFile = "test.json";
text = fileread(myJsonFile);
data = jsondecode(text)
data = struct with fields:
    flowSegmentData: [1×1 struct]
% Access to the next level
fieldnames(data.flowSegmentData)
ans = 9×1 cell array
    {'frc'               }
    {'currentSpeed'      }
    {'freeFlowSpeed'     }
    {'currentTravelTime' }
    {'freeFlowTravelTime'}
    {'confidence'        }
    {'roadClosure'       }
    {'coordinates'       }
    {'x_version'         }

-------------------------Off-topic interlude, 2024-------------------------------

I am currently looking for a job in the field of CV algorithm development, based in Shenzhen, Guangdong, China,or a remote support position. I would be very grateful if anyone is willing to offer me a job or make a recommendation. My preliminary resume can be found at: https://cuixing158.github.io/about/ . Thank you!

Email: cuixingxing150@gmail.com

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cui,xingxing 2023-8-24

Luckily, my expectations above (readstruct support for json reads, writestruct support for json saves) have been implemented by the new version, which has been supported since R2023b!

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