Unwanted line on plot

Question

Steve 2012-2-28

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https://ww2.mathworks.cn/matlabcentral/answers/30474-unwanted-line-on-plot

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?

EDIT: Adding the complete example

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

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Jan 2012-2-28

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.

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Answer 1

Jiro Doke 2012-2-29

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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

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Answer 2

Steve 2012-2-28

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https://ww2.mathworks.cn/matlabcentral/answers/30474-unwanted-line-on-plot#answer_39032

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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.

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Answer 3

Jiro Doke 2012-2-29

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https://ww2.mathworks.cn/matlabcentral/answers/30474-unwanted-line-on-plot#answer_39057

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[Old Answer]

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.

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Answer 4

Steve 2012-2-29

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https://ww2.mathworks.cn/matlabcentral/answers/30474-unwanted-line-on-plot#answer_39061

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.