Unwanted line in on plot

I have two arrays about x-axis and y-axis and plot(x,y) shows following graph.

After I combine two arrays into one by doing data=[x,y], plot(data) has strange brown diagonal line. X,Y axis is also changed.

How can I change second plot to original plot with combined array?

Answer 1

[Walter Roberson]

When you plot() an array that has two columns, that does not mean that the first column should be used for x and that the second column should be used for y. Instead what it means is the same as

plot(1:size(data,2), data(:,1), 1:size(data,2), data(:,2))

That is, each column is used as y coordinates the the x coordinate is the row number. One line is plotted per column.

[Gyeongtae]

thank you. I thought first column of array should be x and second column be y. Then could you what causes the unwanted brown line on plot?

[Walter Roberson]

MATLAB automatically uses the next available colors when you plot multiple lines. It looks to me as if that line corresponds to your second column of data.

[Gyeongtae]

Yes. You're right. The linear-like graph is come from second column. I understand! Thank you Walter :)