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### 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,
display, choices = c(1,2), ...) {
## handle x, which we try with scores, but also retain past usage of
## a two column matrix
X <- if (is.matrix(x)) {
nc <- NCOL(x)
if (nc != 2L) {
stop("a two-column matrix of coordinates is required")
}
x
} else {
if (inherits(x, "envfit")) {
scores(x, display = "vectors", ...)[, 1:2, drop = FALSE]
} else {
scores(x, display = display, choices = choices, ...)
}
}
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)
}
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