Help with "find" (possibly inside of "eval"?)

Asked by Jeffrey McCoy on 20 Jul 2011

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Hi everyone:

Here is my issue...

I am inputting numerous text files inside of a FOR loop in order to pull two particular columns out, one with all characters and one with numbers (double). The code that I have so far, copied below, works as desired. Note that I set "numsvns" as only one entry for debugging.

numsvns = [61]; %only one number for debugging purposes

home_path = path;

for i = 1:length(numsvns)

    % Set the current SVN number as an integer
    svn1 = numsvns(i);
    % Change the path to the folder of the current SVN
    % % Convert the integer SVN to a string
    svn = int2str(svn1);
    % % Append the SVN to the folder needed to open
    directory = strcat('output/sv',svn);
    % % Open the folder for the current SVN
    path(home_path,directory)
    % Open the file and turn the data into a cell array
    fid = fopen('groundVisibilityEvents.txt');
    eval(['gve' svn ' = textscan(fid,''%s %s %f %f %s %s %s %f'');'])
    % Pull out the data of interest (site (col. 1) and duration (col. 8))
    eval(['site' svn ' = gve' svn '{1};'])
    eval(['duration' svn ' = gve' svn '{8};'])
end

This creates two variables of importance, one called "site61" with ASCII characters and one called "duration61" with the double times. Of course, the variables have the 61 appendix since I set "numsvns" = 61 alone.

My next step is to search through "'duration' svn" (in this case, "duration61") in order to find the indices of zero terms. The following works great, as expected:

index = find(duration61==0);

However, I cannot figure out how to generalize this inside of my FOR loop. The following commands don't work, because the "find" function interprets the "duration61" as a character string rather than array:

index = find(['duration' svn]==0);

or, eval(find(['duration' svn]==0));

or, eval(find(['duration' str2num(svn)]==0));

or, abc='duration61'; find(abc==0);

etc.

Is there a way to turn a string into a variable? I thought that "eval" should have done that, but no luck. Otherwise, how do I generalize the "find" command to work with a generic "duration##", where the ## is specified in the loop?

Thank you,

Jeff

1 Comment

Andrew Newell on 20 Jul 2011

Have a look at http://www.mathworks.com/matlabcentral/answers/7885-tutorial-how-to-format-your-question.

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Answer by Andrew Newell on 20 Jul 2011

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Read this FAQ.

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Answer by Jan on 20 Jul 2011

Do not insert the index in the name of the variable. Better use and index as index: "duration{61}" is more powerful and avoids the ugly EVAL stuff.

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Help with "find" (possibly inside of "eval"?)

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