Using eval versus other methods
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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
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Accepted Answer
Jan
on 20 Apr 2011
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.
4 Comments
More Answers (1)
Walter Roberson
on 19 Apr 2011
eval() is the wrong approach the vast majority of the time. Please see
and
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