# Unwanted line on plot

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Steve on 28 Feb 2012
I am plotting real time data and I have a continually updating plot. I want to show 50 points on the graph and update as more data comes in. Here is currently what I am doing:
while 1
for i=1:50
plot(x,y)
end
end
Now the problem with this is that once the for loop gets back to the first element, on the plot there is a line that connects the left most data point to the right most data point and continues until the program is stopped.
Is there anyway to get around this line?
count = 0;
while count < 3
for i = 1 : 30
num1 = rand + 1;
Out1(i) = num1;
c=clock;
Time(i)=(c(5)+(c(6)/100));
plot(Time,Out1)
drawnow();
end
count = count + 1;
end
Jan on 28 Feb 2012
The posted code does not reproduce the problem, because x and y are not defined. Perhaps you simply wand "plot(x,y,'0')", but this is not clear.

Jiro Doke on 29 Feb 2012
Is this what you're looking for?
count = 0;
Out1 = nan(1, 30);
Time = nan(1, 30);
while count < 3
for i = 1 : 30
num1 = rand + 1;
c=clock;
Out1 = [Out1(2:end), num1];
Time = [Time(2:end), (c(5)+(c(6)/60))];
plot(Time,Out1)
pause(0.1);
end
count = count + 1;
end

Steve on 28 Feb 2012
Sorry about that. Here is an example of what I am doing:
count = 0;
while count < 3
for i = 1 : 30
num1 = rand + 1;
Out1(i) = num1;
c=clock;
Time(i)=(c(5)+(c(6)/100));
plot(Time,Out1)
drawnow();
end
count = count + 1;
end
A Once the array reloops to the beginning, there is a line connecting the first point to the latest/newest point. I can kind of understand why, but I guess I just don't have a clue how to get around this.

Jiro Doke on 29 Feb 2012
You're seeing that behavior because you have data points remaining from the previous loop. You can reset the variables Out1 and Time.
count = 0;
while count < 3
Out1 = nan(1, 30);
Time = nan(1, 30);
for i = 1 : 30
num1 = rand + 1;
Out1(i) = num1;
c=clock;
Time(i)=(c(5)+(c(6)/100));
plot(Time,Out1)
drawnow();
end
count = count + 1;
end
BTW, this is called Preallocation which is a good practice when you're assigning values to an array in a loop.

Steve on 29 Feb 2012
Thanks for the response. However, once 30 points fill the graph, what I want to do is continually update the graph. So when data point 31 comes in I want the first point to go away. So overally once the graph fills with data, I don't want to reset the graph.
Steve on 29 Feb 2012
This is exaclty what I am looking for. Thank you!!