IN MATLAB: How to plot a graph every 3 lines from a Text file? - matlab

Question

I have a large text file with 2 columns where the values are separated by commas. I am trying to create a simple program which allows to plot a graph with the data extracted for every 3 rows consecutively until reaching the end of the file.
The first 9 rows of my file can be seen below:
115,1.2
324,3.4
987,1.2
435,-2.3
234,1.4
278,1.3
768,3.4
345,-1.3
126,3.6
I have been reading that with 'Textread' I can write my data into multiple outputs and then I can use 'plot', to plot the previous generated outputs on a graph. I know that I will need some loop whiles to repeat the process and indicate the end of the file, etc. But I am struggling to find the way to do this:-(.
I have only managed plotting a graph for the first 3 rows of my file (see code below), but I need this process to be repeated until the end of the file.
[Codes,Values]=textread('MyData.txt','%3u %f',3,'delimiter',',','emptyvalue',NAN); %//Reads the first three rows of my file and stores the values in 2 variables
figure
plot(Codes,Values) %//plots a graph with the variables obtained before
saveas(gcf,'Graph.pdf') %//Saves the created graph in a pdf format file.
I would be very grateful if somebody could help me.

Answer 1

I have finally found out a way. I paste here the code that allows me plotting a graph every three lines from my text file.
[Codes,Values]=textread('MyData.txt','%3u %f','delimiter',',','emptyvalue',NAN); %//Reads my text file and stores the values in 2 variables
nrows=1;
conta=1;
contb=3;
contc=1;
contd=3;
nfig=1;
while nrows<=size(Codes,1)
if contb<=size(Codes,1)
Codes1=Codes(conta:contb,1);
Values1=Values(contc:contd,1);
figure
plot(Codes1,Values1) %//plots a graph with the selected rows.
saveas(gcf,strcat('Graph', num2str(nfig),'.pdf')) %//Saves the created graph in a pdf format file.
else
Codes1=Codes(conta:contb,1);
Values1=Values(contc:contd,1);
figure
plot(Codes1,Values1) %//plots a graph with the selected rows.
saveas(gcf,strcat('Graph', num2str(nfig),'.pdf'))
end
nrows=nrows+3;
conta=conta+3;
contb=contb+3;
contc=contc+3;
contd=contd+3;
nfig=nfig+1;
end

Answer 2

You mentioned that it is a large text file, but will it an issue to load the whole text file and then simply sample every third row, for example, as follows:
[Codes, Values] = textread('MyData.txt','%3u %f','delimiter',',','emptyvalue',NAN);
rowstokeep = 1:3:length(Values) % every third line
plot(Codes{rowstokeep}, Values{rowstokeep}); % plot just the rows you wanted