Today
Writing to files
Reading from files
Plot function
Lecture 08 Files, Plotting
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File I/O and Plotting in MATLAB, Slides of Computer Programming
An overview of working with files and plotting data in matlab. Topics covered include opening and closing files, reading and writing data, and creating plots using file data. Examples are given for creating and appending data to a file, as well as reading data from a file to create plots.
Typology: Slides
2012/2013
1 / 20
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Today
Writing to files
Reading from files
Plot function
Opening a File - fopen
fopen
Opens a file
f = fopen('cs1109.txt','w');
Usage
fid = fopen(filename); fid = fopen(filename, permission);
% returns id's of all open files fids = fopen('all');
Writing to a File
fprintf
Writes formatted data to the file
fprintf(f, '%d %10.5f', n, x);
Usage
count = fprintf(fid, format, A, ..);
Closing a File
fclose
Closes a file
fclose(f);
Usage
status = fclose(fid);
% closes all open files status = fclose('all');
Appending to a File - Example
Sine Table
deg = 91:180; rad = deg (^) * pi/180; s = sin(rad);
% let's open a file f = fopen('sintable.txt','w');
% write values to the file for j = 1:length(deg) fprintf(f,'%2d %8.6f\n',deg(j),s(j)); end
% and close it! fclose(f);
Writing to a File - Batch Version
fprintf is talented
deg = 0:90; rad = deg (^) * pi/180; s = sin(rad);
% let's open a file f = fopen('sintable.txt','w');
% write values to the file data = [deg; s]; fprintf(f,'%2d %8.6f\n',data);
% and close it! fclose(f);
Reading from a File - Example
Sine Table
% let's open a file for reading f = fopen('sintable.txt','r');
% read values from the file [data, count] = fscanf(f,'%d %f', [2 inf]);
% let's display the values disp(data)
% and close it! fclose(f);
Plotting - Ithaca Weather
Read data from file
Ithaca Temperature June 2012
Day Max Min Avg
f = fopen('ithaca june 2012.txt','r'); data = fscanf(f, '%d %d %d %d',[4 inf]); fclose(f);
Plotting - Ithaca Weather
(^600 5 10 15 20 25 )
65
70
75
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85
90
95
% plot with stars in red color plot(data(1,:),data(2,:),'r*');
Plotting - Ithaca Weather
(^600 5 10 15 20 25 )
65
70
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90
95
% connect data points, use circles plot(data(1,:),data(2,:),'ro−');
Plotting - Figure - Example
Example
figure(1) % plot max temp plot(data(1,:),data(2,:),'r')
figure(2) % plot min temp plot(data(1,:),data(3,:),'b')
figure(3) % plot avg temp plot(data(1,:),data(4,:),'g')
Plotting - hold on/off
hold on
holds the current plot
figure hold on plot(data(1,:),data(2,:),'r') plot(data(1,:),data(3,:),'b') plot(data(1,:),data(4,:),'g') hold off % back to normal state
Plotting - Title/Label
(^400 5 10 15 20 25 )
50
60
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100 Ithaca Daily Temperature − June 2012
Days of June 2012
Temperature (F)
title('Ithaca Daily Temperature − June 2012') xlabel('Days of June 2012') ylabel('Temperature (F)')
Plotting - Legend
(^400 5 10 15 20 25 )
50
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100 Ithaca Daily Temperature − June 2012
Days of June 2012
Temperature (F)
Max Min Avg
legend('Max','Min','Avg')