R devel - Jun 2017 - arrows: no vectors for "code" and "angle" parameters

I was teaching new R users to make some fun graphs. I had some arrows examples
worked up we came across a problem.  The arrows function ignores 2nd
and following elements of vectors given as code an angle.

Would you please consider 1) allowing vectors for code and angle, or
2) returning an error or warning when user mistakenly supplies a
vector for those parameters?  When code like this is wrapped into an
Sweaved document--we I don't see the graph on the screen--this error
is difficult to catch while proofreading.

Example:

x0 <- c(-1, -4, 4.5)
y0 <- c(-1, -4, -8)
x1 <- c(2, -2, -3)
y1 <- c(4, 4, 18)
mylengths <- c(0.2, 0.3, 0.15)
mycodes <- c(3, 2, 1)
myangle <- c(10, 60, 80)

plot(x = c(-5, 5), y = c(-10, 20),
     type = "n", xlab = "", ylab = "")

arrows(x0 = x0, y0 = y0, x1 = x1, y1 = y1,
       length = mylengths, code = mycodes, angle = myangle)

I found a workaround, but this is more difficult to explain to beginners...

plot(x = c(-5, 5), y = c(-10, 20),
     type = "n", xlab = "", ylab = "")

mapply(arrows, x0 = x0, y0 = y0, x1 = x1, y1 = y1,
       length = mylengths, angle = myangle, code = mycodes)

pj

-- 
Paul E. Johnson   http://pj.freefaculty.org
Director, Center for Research Methods and Data Analysis http://crmda.ku.edu

To write to me directly, please address me at pauljohn at ku.edu.

Hi

I have added a warning (r-devel r72811).

I did this rather than allow vectors for length/angle/code because ...
- consistency with (implicit) description of arguments in help page
- backward compatibility (or at least no risk of not-backwards-incompatible)
- it was easier

Note that it is only the length/angle/code that are scalar, e.g., the 
graphical parameters ARE recycled ...

arrows(x0 = x0, y0 = y0, x1 = x1, y1 = y1,
        length = mylengths, code = mycodes, angle = myangle,
        col = 1:3, lwd=1:3, lty=1:3)

Thanks for the report and suggestion.

Paul

On 20/06/17 09:58, Paul Johnson wrote:
> I was teaching new R users to make some fun graphs. I had some arrows
examples
> worked up we came across a problem.  The arrows function ignores 2nd
> and following elements of vectors given as code an angle.
> 
> Would you please consider 1) allowing vectors for code and angle, or
> 2) returning an error or warning when user mistakenly supplies a
> vector for those parameters?  When code like this is wrapped into an
> Sweaved document--we I don't see the graph on the screen--this error
> is difficult to catch while proofreading.
> 
> Example:
> 
> x0 <- c(-1, -4, 4.5)
> y0 <- c(-1, -4, -8)
> x1 <- c(2, -2, -3)
> y1 <- c(4, 4, 18)
> mylengths <- c(0.2, 0.3, 0.15)
> mycodes <- c(3, 2, 1)
> myangle <- c(10, 60, 80)
> 
> plot(x = c(-5, 5), y = c(-10, 20),
>       type = "n", xlab = "", ylab = "")
> 
> arrows(x0 = x0, y0 = y0, x1 = x1, y1 = y1,
>         length = mylengths, code = mycodes, angle = myangle)
> 
> I found a workaround, but this is more difficult to explain to beginners...
> 
> plot(x = c(-5, 5), y = c(-10, 20),
>       type = "n", xlab = "", ylab = "")
> 
> mapply(arrows, x0 = x0, y0 = y0, x1 = x1, y1 = y1,
>         length = mylengths, angle = myangle, code = mycodes)
> 
> pj
> 
-- 
Dr Paul Murrell
Department of Statistics
The University of Auckland
Private Bag 92019
Auckland
New Zealand
64 9 3737599 x85392
paul at stat.auckland.ac.nz
http://www.stat.auckland.ac.nz/~paul/