CODEWITHSUNDEEP
rplot
Sarah West
Sarah West

Reputation: 2037

Change arrowhead of arrows()

i wonder if it is possible to change the arrowhead of an arrow drawn with arrows(). I looked through the documentation but all I found is that I can change the end of a line but not of an arrow?

plot(c(1:10))
arrows(0,0,10,10)

Any help is appreciated :)

Upvotes: 28

Views: 29832

Answers (3)

Greg Snow
Greg Snow

Reputation: 49640

If the other answers don't give you enough control of your arrows using the arrows function, you can use the function my.symbols, from TeachingDemos package. This allows you to create your own custom arrows and plot them.

The function ms.arrows, in the same package, shows one method of doing this: you can modify that function (or other ms.* functions) to create any type of arrow you want, and later use my.symbols to plot them.

Edit

Here is an example as requested:

library(TeachingDemos)

ms.arrowhead <- function(angle, ...) {
  xy <- cbind( c(-1, -0.75, -1, 0), 
               c(-0.5, 0, 0.5, 0) )
  xy <- xy %*% matrix(c(cos(angle),-sin(angle),sin(angle),cos(angle)), 2)
  xspline(xy, shape=c(0, -1, 0, 0), open=FALSE, ...)
}

plot(1:10, 1:10)
my.symbols(1:10, 1:10, ms.arrows, angle=seq(pi, 0, length=10),
           col='blue', adj=1, length=0, symb.plots=TRUE)
my.symbols(1:10, 1:10, ms.arrowhead, angle= seq(pi, 0, length=10), 
           col='green', inches=0.5, lwd=2, symb.plots = TRUE)

This uses the xspline function to draw a triangle with a curved back as the arrowhead. The points can be modified to get a different shaped arrowhead, or another method can be used for the shape.

Upvotes: 6

Andy Barbour
Andy Barbour

Reputation: 8893

Karline Soetaert's package shape is useful for this purpose:

library(shape)
plot(c(0,2),c(-2,2), col=NA)
Arrows(c(0,1.7),c(1.3,-1.8),c(0.8,1.1),c(1.2,-1), lwd=2)

The default is a filled, curved arrowhead that's pleasant to look at:

enter image description here

Gotta love CRAN!

Upvotes: 19

Joris Meys
Joris Meys

Reputation: 108523

as explained in ?arrow , you can use length and angle to change the appearance of standard arrows. With lwd you can change the thickness, exactly like in lines(). Also lty works, although the result is often not exactly nice.

A whole set of examples : 

plot(c(0:10),type="n")

arrows(1,0,2,1,length=0.2,angle=20)
arrows(1,1,2,2,length=0.1,angle=40,lwd=3)

invisible(mapply(arrows,
        rep(c(3,6),each=4),rep(3:6,2),
        rep(c(5,8),each=4),rep(5:8,2),
        angle=seq(10,40,length.out=8),
        length=rep(seq(0.1,0.3,length.out=4),2),
        lwd=rep(1:4,each=2))
)

Upvotes: 20

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