R/ordiArrowMul.R

In pattakosn/Rworkshop: Community Ecology Package

### Scaling of arrows to 'fill' a plot with vectors centred at 'at'.
### Plot dims from 'par("usr")' and arrow heads are in 'x'.
`ordiArrowMul` <-
    function (x, at = c(0,0), fill=0.75) 
{
    u <- par("usr")
    u <- u - rep(at, each = 2)
    r <- c(range(x[,1], na.rm = TRUE), range(x[,2], na.rm = TRUE))
    ## 'rev' takes care of reversed axes like xlim(1,-1)
    rev <- sign(diff(u))[-2]
    if (rev[1] < 0)
        u[1:2] <- u[2:1]
    if (rev[2] < 0)
        u[3:4] <- u[4:3]
    u <- u/r 
    u <- u[is.finite(u) & u > 0]
    fill * min(u)
}