documenation for arrows() is backwards (PR#7839)
hoffman.mm+R-project.org@ebi.ac.uk writes:
Full_Name: Michael Hoffman
Version: 2.1.0
OS: Linux (Fedora Core 3, kernel 2.6.11-1.14_FC3)
Submission from: (NULL) (193.62.199.8)
help(arrows) says:
"""
arrows(x0, y0, x1, y1, length = 0.25, angle = 30, code = 2,
col = par("fg"), lty = NULL, lwd = par("lwd"), xpd = NULL)
...
If 'code=2' an arrowhead is drawn at '(x0[i],y0[i])' and if
'code=1' an arrowhead is drawn at '(x1[i],y1[i])'. If 'code=3' a
head is drawn at both ends of the arrow. Unless 'length = 0',
when no head is drawn.
"""
If you do:
plot(c(-1, 1), c(-1, 1), col=0)
arrows(x0=0, y0=0, x1=0, y1=1, code=2)
it is pretty clear that the arrowhead is drawn at x1, y1 with code=2. If you
switch to code=1, the arrowhead is drawn at x0, y0. Either the documentation or
the function is incorrect.
One way to decide is to compare with Splus. Now that doesn't have a 'code' argument and the arguments are named x1,y1,x2,y2 (I wonder why R wanted to be different here?), but they do put the arrowheads at the *to* end, which does seem to be the sensible thing to do. Arguably, using 'code=2' as the default is a bit weird, but changing it could be quite painful. I.e., we should fix the docs. BTW, the docs also might say that code=0 makes arrows behave like segments(). It is also a bit strange that the code argument isn't vectorized, which might have been useful.
O__ ---- Peter Dalgaard Blegdamsvej 3 c/ /'_ --- Dept. of Biostatistics 2200 Cph. N (*) \(*) -- University of Copenhagen Denmark Ph: (+45) 35327918 ~~~~~~~~~~ - (p.dalgaard@biostat.ku.dk) FAX: (+45) 35327907