Read a userid file and search for userid.json in directory and then search json file

I know what I need to do, just having a hard to getting it going.

I have this userid.txt file that contains the only user files that I want to consider. If the userid say, 1821407, matches a json file within the directory, for example 1821407.json (all json files have this format), I want to check in the file for some data. I'm thinking I can do the search within the json file part. How do I use Matlab to perform the userid comparison within the directory?

Answer 1

[Benjamin Kraus]

I suspect you want to use the dir command to get a list of files in the directory, remove ".json" from the end of the file names, then search that list for your target user IDs.

Something like this perhaps:

userIDs = readmatrix('userids.txt');
jsonFiles = dir('*.json');
jsonFileNames = string({jsonFiles.name});
jsonFileUserIDs = extractBefore({jsonFiles.name},".json");
fileExistsForUserID = ismember(string(userIDs), jsonFileUserIDs);
filesWithUserIDInList = ismember(jsonFileUserIDs, string(userIDs));
jsonFilesFromList = jsonFileNames(filesWithUserIDInList);
for f = 1:numel(jsonFilesFromList)
    fileName = jsonFilesFromList(f);
    data = readstruct(fileName);
    % Do whatever you want with the data here.
end

[Sunshine]

Thank you for your insight. I was able to take this code and pull out json info. Your help is very much appreciated.

Answer 2

[VINAYAK LUHA]

Hi Sunshine,

To find the .JSON files with filenames same as the ones in your "userids.txt" file, you may use the MATLAB "textscan" function as follows -

fileID = fopen('userids.txt', 'r');
userIDs = textscan(fileID, '%s');
fclose(fileID);

userIDs = userIDs{1};

% Find uniqueUserIds since some userIds in your list are repeated eg. -226340
uniqueUserIDs = unique(userIDs);

jsonFiles = dir('*.json');

for i = 1:length(uniqueUserIDs)
    userID = uniqueUserIDs{i};
    jsonFileName = strcat(userID, '.json');
 
    if ismember(jsonFileName, {jsonFiles.name})
        fprintf('File %s found.\n', jsonFileName);
    else
        fprintf('File %s not found.\n', jsonFileName);
    end
end

Further, to search within the .JSON files, you can use the MATLAB "fileread" and "jsondecode" functions, For more details refer to the following documentations -

1. textscan - https://www.mathworks.com/help/matlab/ref/textscan.html
2. fileread-https://www.mathworks.com/help/matlab/ref/fileread.html
3. jsondecode-https://www.mathworks.com/help/matlab/ref/jsondecode.html

Hope this helps.

Regards,

Vinayak

[Sunshine]

Thanks for your response. The userids that are repeated in the userid files are re-appearing in the results. How do I remove the repeats?

[VINAYAK LUHA]

Hi Sunshine,

You can replace the "userIDs" array with the "uniqueUserIDs" array within the loop in the code.

I have also updated my code to reflect this change.

[Sunshine]

Thank you. The update does uniquely identify json file names that are within my userid file. I appreciate your assistance.