Writting data to text file (json)

I am trying to write images annotation information to a text file in json format for futher usage in another programming language. I am not well versed in MATLAB therefore I've been stuck in finding a solution to my problem even after querying the web. The annotations and images are available from this link.

I have attached a sample of the required format in which the information should be extracted. I hope somone can help me out with a script which would serve my purpose.

Thank you.

Answer 1

[Chris]

See jsonencode()

To write the encoded data "encoded" to file:

fid = fopen('file.json','w');
fprintf(fid,'%s',encoded);
fclose(fid);

For a bit more detail on the file handling:

https://www.mathworks.com/matlabcentral/answers/504472-how-to-update-json-file-with-matlab

[Nagesh Ardjoon]

Thank you for your answer, I cam across the jsonencode utility but I am having issues extracting the information from the .mat file and printing it in the required format as attached in my previous post. Appreciate if you could help in achieiving the latter.

[Chris]

Okay, converting the map to the json structure in your example .txt is difficult for a couple reasons:

1. You only need a subset of the values, so the structure needs to be rewritten.
2. Matlab variables can't begin with a number, and all the keys begin with a number.
3. Some classifications have other characters that are invalid for variable names.

Is it okay to rename keys (e.g., append a 'k' in front of each one) and food types ("patate/pure" -> "patate_pure" ?

[Chris]

Here's a dirty hack that should do it.

load('annotations.mat');
keys = annotations.keys;
v = annotations.values;

fid = fopen('out.json','a');

for idx = 1:numel(keys)
    numtypes = size(v{idx},1);
    thisstr = ['{"',keys{idx},'": ['];
    for jdx = 1:numtypes
        tempstr1 = join(['{"',char(v{idx}{jdx,2}),'": {"BR": [',string(v{idx}{jdx,5}).join(", "),']'],'');
        tempstr2 = join([', "BB": [',string(v{idx}{jdx,6}).join(", "),']}'],'');
        if jdx == numtypes
            thisstr = join([thisstr, tempstr1,tempstr2,'}]}'],'');
        else
            thisstr = join([thisstr, tempstr1,tempstr2,'},'],'');
        end
    end
    fprintf(fid,'%s\n',thisstr);
end
fclose(fid);

[Nagesh Ardjoon]

Thank you for your help Chris, I came up with something similar but a lot less elegant. I initially thought there would be some sort of built in functions to address my problem but as you confirmed in your previous post there are certain constraints which limits their usage.

[Pippa Williams]

Hi folks,

I have a similar issue, but I need the variable names to start with a number (I cannot change these). I'm assuming the only way is to put some identifier at the start of the variable name which can be easily deleted afterwards. Is there a better solution I'm not thinking of?

e.g. if the variable name is 30min_horizon, I'll use something like NUMNAME_30min_horizon.

Then use: erase(jsonstring,"NUMNAME_");

Thanks for your help so far!

Pippa

[Chris]

Hi Pippa,

If you can do that, it's pretty clever and likely one of the easiest solutions.

You could possibly try constructing a loop like the one three posts up (or a more comprehensive, error-tolerant set of functions, if you'll be doing this often), but if you're dealing with a map or struct and are able to insert that prefix without trouble, that would be the approach I'd take.

If you're still having trouble, feel free to post a new question and upload or point to some example data. Someone with relevant experience might see it on the front page and have a different answer.