Question

Is it possible to add arrows using locator? I gave it a try but no luck….

plot(1:3)
arrows(x0=locator(1), x1=locator(1),
       y0=locator(1), y1=locator(1), code=1)#single headed arrow

Answer 1

If you look at what locator(1) returns you’ll see why this isn’t even close to working:

> locator(1)
$x
[1] 1.365533

$y
[1] 2.25695

So you were passing a list of length two to each argument. I would probably (though this won’t be reproducible so I wouldn’t really do it in anger in any analysis) approach this via:

> locs <- locator(2)
> locs
$x
[1] 1.265845 1.587567

$y
[1] 2.604642 2.267028

The add the arrow using the data saved in locs:

with(locs, arrows(x0=x[1], x1=x[2], y0=y[1], y1= y[2], code=1))