importing a csv file into matlab automatically after it gets changed

I have .csv file on my desktop which get replaced. I want to use a command in matlab which imports this file every time it gets changed into matlab for calculations. I got this formula:

fsw = System.IO.FileSystemWatcher();
fsw.Path = 'C:\Users\wolfx\Desktop';
fsw.Filter = 'filename.csv';
fsw.EnableRaisingEvents = true;
listenerhandle = addlistener(fsw, 'Changed', importfcn);
%signature of importfcn is function importfcn(sender, eventargs)
%add a small delay in importfcn before reading the file as the event is raised
%to make sure that file modification is complete

This formula gives me the error Undefined function or variable 'importfcn'.

Can anyone give me a hint or a site where I can read more about this?

thanks

[Geoff Hayes]

AA - is your function importfcn defined in the MATLAB search path? In the Command Window type

 which importfcn -all

to see where this file is located. If it isn't found, then you must add the folder that contains this file to the search path.

[AA]

how can i find this file and add it to the search path??

[Geoff Hayes]

Isn't importfcn a function that you have created? In a previous post of yours, http://www.mathworks.com/matlabcentral/answers/163047-automatic-import-into-matlab-after-time-period, Guillame's answer included the following code

 t = timer;
 t.Period = 49 * 60;
 t.TimerFcn = importfcn; %for you to define with signature: function  
                         % importfcn(obj, event)

Note his comment - you have to define the function with the specified signature. Since you accepted his answer, then you must have created this file and so you must know which folder has it. So once you have found the file, you can add its folder to the search path in any number of ways, including using addpath.

[AA]

I didnt create the function file importfcn. that is why i cannot find it. how can i create this function file? i have never done this before.

Answer 1

[matt dash]

The errror is because when you just type "importfcn" it is attempting to RUN importfcn. What you're trying to do is tell the addlistener function "the NAME of the function i want you to run is "importfcn". You do this with the @ symbol. Thus you want:

listenerhandle = addlistener(fsw, 'Changed', @importfcn);

[AA]

ok that looks great but when I run the file then nothing happens meaning when I type in the variable kevin into the command window then i get the response unknown variable. This function is supposed to import the data and present itself as kevin. on the other hand if i type in the function importfcn then i get kevin = matrix values but I cannot use this as independent variable for further calculations. I need the imported data for further calculations.

[matt dash]

Ah, yes, that would be the "do something with the data" comment in Geoff's code above. If you're trying to send the data back to the base matlab workspace, look at the "assignin" function, which you can use in the importfcn variable to define a variable in the base workspace. E.g.

assignin('base','kevin',kevin)

[AA]

function importfcn(obj, event)
 % wait an extra second to ensure that the file modification is complete
 pause(1.0);
 % read the data from file
 fileToRead = fullfile('C:\Users\wolfgang\Desktop\NZDUSD1.csv');
 circa = xlsread(fileToRead);
 kevin=0.5*(circa(:,4)+circa(:,5)).'
assignin('base','kevin',kevin) 
 % do something with the data
end

fsw = System.IO.FileSystemWatcher();
fsw.Path = 'C:\Users\wolfgang\Desktop';
fsw.Filter = 'NZDUSD1.csv';
fsw.EnableRaisingEvents = true;
listenerhandle = addlistener(fsw, 'Changed', @importfcn);
%signature of importfcn is function importfcn(sender, eventargs)
%add a small delay in importfcn before reading the file as the event is raised
%to make sure that file modification is complete

Answer 2

[Geoff Hayes]

AA - try creating a function as follows (saving this to file as importfcn.m or as a nested function within your other code)

 function importfcn(obj, event)

 % wait an extra second to ensure that the file modification is complete
 pause(1.0);

 % read the data from file
 fileToRead = fullfile('C:\Users\wolfx\Desktop','filename.csv');

 data = csvread(fileToRead);

 % do something with the data

If you nest the function, then you can make use of fsw.Path and fsw.Filter in building the fileToRead and not have to hard-code the path and file name.