MATLAB: Using eval versus other methods

evalfaq 4.6multiple fileswind

Hello,
I am currently working on a script to automate some number crunching and am wondering if there is a better (more efficient) way to write the code without having to use eval.
Our main problem is using the dates in the file names as variables and being able to index correctly while performing various functions.
Thank you for your help,
Dan the Man
%load in all 1 minute averaged files and perform calculations and generate
%plots
%--------------------------------------------------------------
%define days of month in text file names, MUST BE CHANGED EVERYTIME YOU
%LOAD IN A NEW GROUP OF FILES!
day = [9, 10];
%import all text files from one directory at once
AVGfiles = dir('*AVG.txt');
for i=1:length(AVGfiles)
eval(['load ' AVGfiles(i).name ' -ascii AVG']);
end
%------------------------------------------------------------------------
for i = 1:length(AVGfiles)
      j = day(i);
      %define length of each file to be used in total wind calculation
      eval(['k = length(Apr' num2str(j) 'AVG)'])
      %compute turbulence for each minute for each text file
      eval(['TKE_' num2str(j) ' = 0.5 * (Apr' num2str(j) 'AVG (:,19) + Apr' num2str(j) 'AVG (:,20) + Apr' num2str(j) 'AVG (:,21))'])
      %compute total wind
      for a = 1:k
          eval(['total_wind_' num2str(j) '(a) = ((Apr' num2str(j) 'AVG (a,7))^2 + (Apr' num2str(j) 'AVG (a,8))^2 + (Apr' num2str(j) 'AVG (a,9))^2)^(1/2)'])
      end
      eval(['mph_wind_' num2str(j) ' = total_wind_' num2str(j) '/100'])
      eval(['mph_wind_' num2str(j) ' = (mph_wind_' num2str(j) ' * 3600) / 1609.344'])
      %compute datenumber for each file to use in plotting
      eval(['datenumber_' num2str(j) ' = datenum(Apr' num2str(j) 'AVG (:,3), Apr' num2str(j) 'AVG (:,1), Apr' num2str(j) 'AVG (:,2), Apr' num2str(j) 'AVG (:,4), Apr' num2str(j) 'AVG (:,5), Apr' num2str(j) 'AVG (:,6))'])
      %generate a TKE plot for each day
      eval(['plot(datenumber_' num2str(j) ', TKE_' num2str(j) ')'])
      datetick('x', 'mm-dd-yyyy')
      ylabel('TKE')
      title(['UNR Roof Apr ',num2str(j),' TKE'],'Fontsize',14)
      saveas(gcf,['Apr_',num2str(j), 'TKE'], 'png')
      %generate a total wind plot for each day
      eval(['plot(datenumber_' num2str(j) ', mph_wind_' num2str(j) ')'])
      datetick('x', 'mm-dd-yyyy')
      ylabel('Wind Speed (mph)')
      title(['UNR Roof Apr ',num2str(j),' Total Wind Speed'],'Fontsize',14)
      saveas(gcf,['Apr_',num2str(j), 'wind'], 'png')
end

Best Answer

Convert:
eval(['load ' AVGfiles(i).name ' -ascii AVG']);
to:
Data = load(AVGfiles(i).name, '-ascii', 'AVG');
Then "Data.(['Apr', num2str(j), 'AVG'])" is much safer and more efficient than the EVAL constructions.
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