Plotting a huge matrix

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Yaser Khojah
Yaser Khojah on 13 Sep 2018
Edited: Yaser Khojah on 14 Sep 2018
I have a big matrix (Supply) with size of 21 X 1000,000 and I want to plot each column against a fixed time vector as
stairs(time, supply)
I have tried to do it with for loop and using the Apps tool box but it is taking forever to run. Is there a fast way to do it?
This is my for loop:
if true
for k = 1:size(supply,2)
stairs(time ,Supply(:,k)); hold on
disp([' ',num2str(k)])
end
Thanks,
  2 Comments
Adam
Adam on 13 Sep 2018
Are you sure you need to plot every value of those 1000000? There is no way that you can distinguish that many values on a plot. Indeed, at that level there aren't enough pixels on the screen to plot them all either. I would recommend sub-sampling your data and plotting that instead. I don't know off the top of my head what is a realistic number of samples to plot that you can visually distinguish, but it would be orders of magnitude less than that.
jonas
jonas on 13 Sep 2018
Edited: jonas on 13 Sep 2018

It could possibly be faster to store the output instead of plotting in each loop. The stairs function will not plot if two output arguments are specified

[x,y] = stairs([1 2 1],[1 2 1])

then you can just plot everything in one go

plot(x,y)

this way, no objects are created until you plot, so the loop should be much faster.

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Accepted Answer

Jan
Jan on 13 Sep 2018
Omit the disp command, because updating the command window 1e6 times wastes a lot of time. Setting hold on repeatedly is not efficient also. Then do not create 1 Millions stairs calls, but call stairs with a matrix:
stairs(time, Supply);
But most of all consider Adam's comment: It is very unlikely that this plot is useful, because it has a huge pixel density.
  9 Comments
Steven Lord
Steven Lord on 14 Sep 2018
[Yaser Khojah wrote the following in a flag on Jonah's first comment on this answer. If you want to respond to a comment please add your own comment rather than adding a flag. The intent of flags is to notify contributors with sufficient reputation of potential unclear, off-topic, or spam messages. Thanks.]
I was able to create the plot without the outliers. However, I get this error "Value should be a finite number greater than 0". I think the outliers should be larger than zero.
jonas
jonas on 14 Sep 2018
Sorry that was bad advice from my part. I just noticed that the outliers were not plotted while missing the error message. This should work:
delete(findobj(gca,'Tag','Outliers'))

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More Answers (2)

Yaser Khojah
Yaser Khojah on 13 Sep 2018
You are all right but I just wanted to see the whole dense lines. I'm using now boxplot instead since I could not show all the lines

Yaser Khojah
Yaser Khojah on 14 Sep 2018
Edited: Yaser Khojah on 14 Sep 2018
If you do not want to include outliers then use this:
if true
boxplot(y,'symbol','')
end

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