[R] How to draw a line in plot when I know the start point(x

[Marc Schwartz]

On Jun 25, 2009, at 1:51 PM, Ted Harding wrote:

> On 25-Jun-09 18:38:37, Marc Schwartz wrote:
>> On Jun 25, 2009, at 1:30 PM, Lesandro wrote:
>>> Hello all,
>>> How to draw a line in plot when I know the start point(x1,y1)
>>> and end point(x2,y2)? I need make this as additional information
>>> in the graph:
>>>
>>> plot(wl2[[1]],wl2[[2]])
>>>
>>> I think that is possible make this with the function abline(), is
>>> possible? I looked the function lines() too, but don't understand
>>> as make.
>>>
>>> Thanks!
>>> Lesandro
>>
>> See ?segments which does just what you are looking for.
>>
>> lines() is more designed for a series of connected lines (eg. a
>> polygon) rather than a single line segment.
>>
>> abline() can draw a straight line, at a given vertical or horizontal
>> position, or if given a linear model object, the fitted line.
>> HTH,
>> Marc Schwartz
>
> Hmm ... for this particular purpose I don't see what is wrong with
>
>  plot(wl2[[1]],wl2[[2]])
>  lines(c(x1,x2),c(y1,y2))
>
> along with any additional paramaters to lines() for line-type,
> colour, etc. -- I do this all the time ...
> Ted.

Nothing wrong at all Ted. It will of course work.

For example:

plot(1:10)
lines(c(2, 4), c(6, 8))

That will give you the same result as:

plot(1:10)
segments(2, 6, 4, 8)


In this case, it may be a matter of choice. For single lines, I tend  
to use segments().

As is frequently the case with R, there is more than one way to skin  
the feline...

Regards,

Marc