MATLAB: How to use datetick for this code

datetickgraphplot

A = textscan(fopen('7633_Flux_AmeriFluxFormat_3.dat'),'%f %f %f %f %f %f %f %f %f %f %f %f %f %f %s %s %f %f %f %f %f %f %f %f %f %f %f %f %f %f %f %f %f %f %f %f %f %f %f %f %f %f %f %f %f %s %s %f %f %f %f %f %f %f %f', 'Delimiter',',','Headerlines',1);
A_time = A{1,1};
B_time = num2str(A_time);
x_serial = datenum(B_time,'yyyymmddHHMM');
x = datetick('x','dd-mmm-yyyy HH:MM:SS','keeplimits')
CO2 = A{1,3};
figure()
plot(x,CO2)

this is the first part of my code. my x-axis is currently in matlab serial numbers. When I try running this, it says there are too many output arguments in the datetick line. I've never used datetick before. Please tell me what i'm doing wrong and how to fix it

Best Answer

I would code it differently:

fidi = fopen('7633_Flux_AmeriFluxFormat_3.dat');
A = textscan(fidi,'%f %f %f %f %f %f %f %f %f %f %f %f %f %f %s %s %f %f %f %f %f %f %f %f %f %f %f %f %f %f %f %f %f %f %f %f %f %f %f %f %f %f %f %f %f %s %s %f %f %f %f %f %f %f %f', 'Delimiter',',','Headerlines',1);
fclose(fidi);
A_time = A{1,1};
B_time = num2str(A_time);
x_serial = datenum(B_time,'yyyymmddHHMM');
CO2 = A{1,3};
figure()
plot(x,CO2)
datetick('x','dd-mmm-yyyy HH:MM:SS','keeplimits')

I do not have your file, so I am stating that this is*_UNTESTED CODE_*. You will have to see if it works.

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MATLAB: Trying to create a loop for for opening data files and plotting them

"I want to change it so that a different file is opened with each loop but i'm not sure how"

By following the guidelines in the MATLAB documentation:

https://www.mathworks.com/help/matlab/import_export/process-a-sequence-of-files.html

So you could either use dir to read the names from a folder, or generate the names using sprintf. Pick whichever works best for you. Here is an example with sprintf:

opt = {'Delimiter',',', 'Headerlines',1};
fmt = ['%s',repmat('%f',1,13),'%s%s',repmat('%f',1,29),'%s%s',repmat('%f',1,8)];
for k = 1:41
    fnm = sprintf('7633_Flux_AmeriFluxFormat_%d.dat',k); % I had to guess the name format
    [fid,msg] = fopen(fnm,'rt');
    assert(fid>=3,msg) 
    A = textscan(fid,fmt,opt{:});
    x = datenum(A{1,1},'yyyymmddHHMM'); % simpler
    ...
end

Note that you did not give any information on how the files names change, so I just guessed that the numbered suffix increments each time: if the names have some other pattern, you will have to specify that yourself, or give us a precise specification, or use dir.

Calling fopen directly inside textscan is an inspired move, but is not recommended: MATLAB does not automatically close those files, so you will end up with a large number of open files, which is not a good idea (it can even crash MATLAB if there are too many). So you should always use fclose if you fopen any file.

Note that your code could be significantly simplified by using readtable.

MATLAB: How to populate a cell with a loop

fmt=[repmat('%f',1,14) repmat('%s',1,2) repmat('%f',1,29) repmat('%s',1,2) repmat('%f',1,8)];   % legible (sorta') format string
d=dir('AppropriateString*.ext');                                  % setup dir() to return the wanted actual files
for i=1:length(d)                                                 % iterate over files found

  fid=fopen(d(i).name),'r');
  A(i)=textscan(fid,fmt,'Delimiter',',','Headerlines',1);
  fid=fclose(fid);
end

Will leave with cell array of one row per file.

Which specific columns are date/time data? The two sets of '%s' I presume?

datenum has been deprecated; better to use datetime instead and easier than textscan would be to use readtable.

Let us know the actual date format/location in the files and we can write specific conversion for it, too...

ADDENDUM

OK, if the string fields are really just 'nan' or variant thereof, use numeric format for them and convert them on input as well.

...
fmt=['%{yyyyMMddHHmmss}D' repmat('%f',1,54)]; % legible format string
for i=1:length(d)                             % iterate over files found
  fid=fopen(d(i).name),'r');
  A{i}=textscan(fid,fmt,'Delimiter',',','Headerlines',1,'collectoutput',1);
    fid=fclose(fid);
  end

using datetime class rather than the deprecated datenum for the date field.

You might also consider readtable depending on what your next step(s) are with these data.

Best Answer

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MATLAB: Trying to create a loop for for opening data files and plotting them

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