How to draw multiple lines (plots) using semilogy() at once?

Hello everyone,

I need to draw multiple lines using semilogy() with unknown input size. What I tried:

• hold on, doesnt work because it's get me ugly formatation: cut off title, and others.

What solution I guess solve my problem? Is make the semilogy function runs with a string input made by strcat().

Ps.: It works when using semiology with manual parameters.

    fileNames
    strSemilogy="";
    for (i = 1:numel(fileNames))
        T{i} = readtable(strcat("../Output/",fileNames(i),".txt")); % this isn't working
        i_ = string(i);
        strSemilogy= strcat(strSemilogy,strcat("T{",i_,"}.snr, T{",i_,"}.bErr,"," '-*'"));
        if (i < numel(fileNames))
           strSemilogy = strcat(strSemilogy, ", ");
        end
    end
    fig = figure(1);
    set(fig,'color',[1 1 1]);
    eval(semilogy(strSemilogy);

Invalid expression. When calling a function or indexing a variable, use parentheses. Otherwise, check for mismatched delimiters.

Answer 1

[dpb]

The answer will NOT be to use eval, but hold on and then make the adjustments you think needed.

Without an example of what you think isn't satisfactory, there's really no way to say what to do, specifically, to solve whatever issue it is that you are having.

Of course, the alternate way is to put all the multiple y values into an array by column and use the builtin vectorized code handle each column automagically. If they're not all the same length, that will require augmenting the array with NaNs to match longest, so takes a little more logic in that case.

But, your attempt looks to be far too overly complicated way to go at it...

PATH="../Output/";                          % don't bury data in code, use variables so can change
d=dir(fullfile(PATH,"*.txt"));              % get the dir() struct of matching files  
for i=1:numel(d)
  T=readtable(fullfile(d(i).folder,d(i).name)); % this will work if the file structure is ok; we don't know that
  hL(i)=semilogy(T.snr,T.bErr,'-*');            % ditto; we don't know what form the variable names are in
  if i==1, hold on, end                         % add subsequent plots to first...
end

Now you'll have all the lines on a single axes with an array of line handles to each that can use to set properties of individual lines, legends, etc., as desired. Also, now is the time/place to add the axis labels, title, any other additional cleanup desired.

We would need to see one of the text files to know any other specific fixes/modifications needed...it's all data-dependent at this point.

Answer 2

[Voss]

It is not necessary to resort to using eval to evaluate a list of arguments stored as a string.

You can store the arguments in a cell array and use brace indexing {:} to pass them to semilogy as a comma-separated list.

% first, I construct a cell array of tables like your variable T:
snr = 1:10;
T = cell(1,5);
for ii = 1:numel(T)
    bErr = rand(1,10);
    T{ii} = table(snr,bErr);
end

% now, build the list of arguments for semilogy:
args = cell(3,numel(T));
for i = 1:numel(T)
    args(:,i) = {T{i}.snr; T{i}.bErr; '-*'};
end

% call semilogy with the argument list:
semilogy(args{:});

https://www.mathworks.com/matlabcentral/answers/1656435-tutorial-comma-separated-lists-and-how-to-use-them

https://www.mathworks.com/help/matlab/matlab_prog/comma-separated-lists.html

[Voss]

@Brendon Peres: Did this answer work for you?