Write a function wich oly needs a file input as argument

function getGPSstats(file)
%cd c:\Users\NMR\Desktop\Ex4_Data;
data = load(file);
% delete the error columns
data(:,7:9)=[];
% create a single vector for ech of the six remaining columns
decYear = data(:,1);
intYear = data(:,2);
dayNum = data(:,3);
eastPos = data(:,5);
vertPos = data(:,6);
% plot the data
plot(data);

I want to write a function wich acepts a .neu file from several GPS Stations. every file has about 4000x9 structure, the last three columns are error columns, so i delete them to save a bit storage.

But when I want to seperate the columns like this

decYear = data(:,1);
intYear = data(:,2);
dayNum = data(:,3);
eastPos = data(:,5);
vertPos = data(:,6);

Matlab told me "The value assigned to .... might be unused

So my function is stored as ans and get plotted at the end. So i wonder what is the issue of the code. I want to have a Matrix called data and modify it, but i ony get ans

*I have to correct myself when i try to call the function like getGPSstats('gpsdata.neu') I don't even get an ans, just the plot.

Answer 1

[David Fletcher]

It's a warning that you have declared variables (decYear, intYear, dayNum etc.) and not used them anywhere in the code. The code will still run, but obviously if the variables aren't ever used, then there isn't much point declaring them in the first place. And yes, all the variables with be local to the function, if you do not declare any output then all you will get out of it will be the plot.

[Niklas Reinshagen]

okay thanks for yor reply but dosen't I stored the loades file in a variable called "data" and can recall this variable later? What would be a possibility to get the prblem fixed?

[David Fletcher]

The data variable will disappear when the function exits, but of course the file will still exist and can be loaded elsewhere. If you want want the actual data variable to exist after the function exits, then it should be defined as a function output. There are other ways, such as using global variables, but I wouldn't advocate their use.

function [data]=getGPSstats(file)

Will pass the data variable out of the function when it exits, or if you want the derived variables:

function [decYear, intYear, dayNum, eastPos, vertPos]=getGPSstats(file)

[Niklas Reinshagen]

honestly I don't get the point. When I put ech line of code piece for piece in the command window, I get exactly what I want to. But in the skript it won't work. I guess the problem is here:

data = load(file);

there is no variable created called data, so matlab cant go on and make other variables based on "data".

Do you have any idea how I can achieve matlab create the varaible "data"?

[Niklas Reinshagen]

soryy I don't saw you gave me an example i try it imediatly

[David Fletcher]

You said you got the plot at the end in your original message: if you got the plot then the data must have loaded into the variable. And if there were no error messages, all the variables derived from data were created, but as I said, unless you declare the variables as function outputs then they will all disappear when the function exits.

function [decYear, intYear, dayNum, eastPos, vertPos]=getGPSstats(file)
    %cd c:\Users\NMR\Desktop\Ex4_Data;
    data = load(file);
    % delete the error columns
    data(:,7:9)=[];
    % create a single vector for ech of the six remaining columns
    decYear = data(:,1);
    intYear = data(:,2);
    dayNum = data(:,3);
    eastPos = data(:,5);
    vertPos = data(:,6);
    % plot the data
    plot(data);
end

Then call the function with

[decYear, intYear, dayNum, eastPos, vertPos]=getGPSstats(filename)

and you will get the variables as function outputs

Answer 2

[Image Analyst]

Does this work:

If not, attach the .neu file (zipped up) so we can try it.

clc;	% Clear command window.
fprintf('Running %s.m ...\n', mfilename);
clear;	% Delete all variables.
close all;	% Close all figure windows except those created by imtool.
workspace;	% Make sure the workspace panel is showing.

folder = 'c:\Users\NMR\Desktop\Ex4_Data';
fullFileName = fullfile(folder, 'gpsdata.neu');
data = getGPSstats(fullFileName);
% Now do something else with data.
fprintf('Done running %s.m\n', mfilename);

%===============================================================================
function data = getGPSstats(fullFileName)
data = []; % Initialize.
if ~isfile(fullFileName)
	errorMessage = sprintf('Error: the file does not exist:\n%s', fullFileName);
	fprintf('%s\n', errorMessage);
	uiwait(errordlg(errorMessage));
	return;
end
%cd c:\Users\NMR\Desktop\Ex4_Data;
data = load(fullFileName); % Maybe use readmatrix() or importdata() instead?
% Delete the error columns.
data(:,7:9)=[];

% Unused code below -- commented out.
% % Create a single vector for ech of the six remaining columns
% decYear = data(:,1);
% intYear = data(:,2);
% dayNum = data(:,3);
% eastPos = data(:,5);
% vertPos = data(:,6);

% Plot the data
plot(data, '-', 'LineWidth', 2);
grid on;
fontSize = 18;
[folder, baseNameNoExt, ext] = fileparts(fullFileName);
title([baseNameNoExt, ext], 'FontSize', fontSize);
xlabel('x', 'FontSize', fontSize);
ylabel('y', 'FontSize', fontSize);
end