How to draw line vertical to Y-axis?

Hey Matlab users,

If a = [1 2 3 4 5 6 7]; and b = [1 4 7 10 7 4 1]; and the plot it by : figure,plot(a,b), how can I draw let's say a red line vertical to the value 4 and 7 in the y-axis (parallel to x-axis)? So that i can see the window between 4 and 7.

Thanks so much in advance,

 Mehdi

Answer 1

[Walter Roberson]

The same as for your previous question. The solution for that was

yL = get(gca,'YLim');
line([3 3],yL,'Color','r');
line([5 5],yL,'Color','r');

and if you are wanting to draw vertical lines at 4 and 7, you would just change the code to

yL = get(gca,'YLim');
line([4 4],yL,'Color','r');
line([7 7],yL,'Color','r');

Perhaps what you want is instead horizontal lines? If so then

xL = get(gca,'XLim');
line(xL,[4 4],'Color','r');
line(xL,[7 7],'Color','r');

[Sven]

Tiny little typo there Walter ;)

But you get my vote anyway for completeness :)

Mehdi, please note that your question title said "vertical" lines, but as Walter has pointed out, you were actually asking for "horizontal" lines

[M G]

Yes that's right, I meant horizontal line. Thanks Walter and Sven.

[Walter Roberson]

Typo? Now you've got me going over it character by character, because I can't find a typo... agggh!

[Sven]

Last line, Walter :)

[Sven]

Ah... so now you go ahead and silently fix the typo just to make me look silly :)

[Gourav Mitra]

it works fine but in some case, the vertical line doesnot fit or cover the entire ylimit.

[Walter Roberson]

These days, see yline()

If you get the current ylim and use it to draw, and then you zoom or pan, then the code I posted back then will not adjust to draw according to the new limits. However, the newer yline() should do that.

Answer 2

[Noushin Farnoud]

If you want to draw a line that spans the entire xlim or ylim of your figure, then I suggest that you use hline or vline functions from: http://www.mathworks.com/matlabcentral/fileexchange/1039-hline-and-vline

You can also plot multiple vertical or horizontal lines at the same time using these functions. For example: hline([5,6,8]) draws 3 horizontal lines at x=5, x=6 and x=8.

Answer 3

[Eric Sargent]

Starting in R2018b you can simply use xline and yline.

In this case:

yline(4,'r');
yline(7,'r');

Answer 4

[Sven]

Hi Mehdi, try this after plotting:

xlims = get(gca,'XLim');
hold on
plot(xlims, [4 4], '-r')
plot(xlims, [7 7], '-r')

[Walter Roberson]

Those would be horizontal lines, not vertical lines...

[Sven]

The questions is a little ambiguous. I went with vertical lines first however note that the questioner wants lines "parallel to x-axis".

[Walter Roberson]

Confusing...

[Sven]

Doh! I voted yours up and now it's above mine... that's a blow to my chances for getting accepted! heheh

Answer 5

[James]

There is an excellent answer over on http://stackoverflow.com/a/8108766/1194420 repeated below for convenience. ---

There exist an undocumented function graph2d.constantline:

plot(-2:5, (-2:5).^2-1)
%# vertical line
hx = graph2d.constantline(0, 'LineStyle',':', 'Color',[.7 .7 .7]);
changedependvar(hx,'x');
%# horizontal line
hy = graph2d.constantline(0, 'Color',[.7 .7 .7]);
changedependvar(hy,'y');

Answer 6

[Wayne King]

a = [1 2 3 4 5 6 7];
b = [1 4 7 10 7 4 1]; 
plot(a,b)
hold on
plot(a,4*ones(length(b)),'r');
plot(a,7*ones(length(b)),'r');

[Walter Roberson]

A bit murky if "a" does not happen to be in sorted order, especially if the drawingmode is set to xor