Access the data from a Struct

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Susan 2020-3-30

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评论： Susan 2020-3-31

I have a struct with fields

val = struct with fields:
       abstract: [1×1 struct]
      body_text: [72×1 struct]

when I extract the text data in body_text using "val.body_text.text" I got 72*1 struct. But when I try "A = val.abstract.text", I got only the first struct of the 72 structs. How can I put all these [72×1 struct] into A?

Thanks!

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Ameer Hamza 2020-3-30

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''so val.abstract.text is either invalid reference or is the name of the 1x1 struct under val.abstract'''

Not necessarily. For example

>> s.text = '123';
s.xyz = 2;
val.abstract = s;
val.body_text = repmat(s, 1, 72);
>> val
val = 
  struct with fields:
     abstract: [1×1 struct]
    body_text: [1×72 struct]
>> val.abstract.text
ans =
    '123'

Susan 2020-3-30

Sorry for the confusion! What I meant was "But when I try "A = val.body_text.text", I got only the first struct of the 72 structs"

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Answer 1

Ameer Hamza 2020-3-30

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https://ww2.mathworks.cn/matlabcentral/answers/514062-access-the-data-from-a-struct#answer_422930

编辑：Ameer Hamza 2020-3-30

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Try this, if the data in the field 'text' is scalar

A = [val.abstract.text];

If it is vector than try

A = {val.abstract.text};

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Susan 2020-3-30

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JSON files.zip

I've got another question regarding the nested struct and your answer would be greatly appreciated.

I have a bunch of .json files, say 1000. To read each files I run the following code

fname = 'C:\Users\...\d90f3c62681e.json';
val = jsondecode(fileread(fname));

then I get

val = 
  struct with fields:
       paper_id: 'd90f3c62681e'
       metadata: [1×1 struct]
       abstract: [1×1 struct]
      body_text: [4×1 struct]
    bib_entries: [1×1 struct]
    ref_entries: [1×1 struct]
    back_matter: []
    
val.abstract = 
  struct with fields:
        text: '300 words) The data ...' 
        cite_spans: []
        ref_spans: []
       section: 'Abstract'
       
val.body_text = 
  4×1 struct array with fields:
    text
    cite_spans
    ref_spans
    section

which the name of each file is the paper_ID. I am only interested in the text data in val.abstract.text and val.body_text.text which their sizes may change from file to file. How can I get all the text data from each file and put them in a single .json files? I have attached 3 .json files from the data set I have. Any input would be greatly appreciated.

Ameer Hamza 2020-3-31

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Try the following code. Place it one directly above the JSON files, or you can modify the first line according to the path of your JSON files. It will read all files, and gather their abstract.text and body_text.text fields into one struct. It then writes the final struct as a JSON file.

files = dir('JSON files/*.json');
s = struct('abstract', [], 'body_text', []);
for i=1:numel(files)
    filename = fullfile(files(i).folder, files(i).name);
    data = jsondecode(fileread(filename));
    if ~isempty(data.abstract)
        s.abstract = [s.abstract; cell2struct({data.abstract.text}, 'text', 1)];
    end
    if ~isempty(data.body_text)
        s.body_text = [s.body_text; cell2struct({data.body_text.text}, 'text', 1)];
    end
end
str = jsonencode(s);
f = fopen('filename.json', 'w');
fprintf(f, '%s', str);
fclose(f);